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  • command&pointer&malloc [closed]

    - by gcc
    input 23 3 4 4 42 n 23 0 9 9 n n n 3 9 9 x //according to input,i should create int pointer arrays. pointer arrays starting from 1 (that is initial arrays is arrays[1].when program sees n ,it must be jumb to arrays 2 expected output arrays[1] 3 4 5 42 arrays[2] 23 0 9 9 arrays[5] 3 9 9 x is stopper n is comman to create new pointer array i am new in this site anyone help me how can i write

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  • mongodb java driver - raw command?

    - by Scott
    Is it possible to execute raw commands as javascript through the Java driver for MongoDB? I'm tired of wrapping everything in Java objects using Rhino, and would happily sacrifice performance for the convenience of passing javascript directly through to the DB. If not, I can always use sleepymongoose or something, but I don't really want to add yet another language (python) to the stack at this point. Any insights are appreciated.

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  • Copying a file with PHP Command

    - by Tom
    Hi, I'm having a problem using the copy function in PHP, what is wrong with it? I get the error; Parse error: syntax error, unexpected T_VARIABLE On the bottom line; $targetDir = 'file.txt'; $targetDir2 = 'file2.txt'; copy($targetDir, $targetDir2); Thanks The entire file is; <?PHP $targetDir = 'file.txt'; $targetDir2 = 'file2.txt'; copy($targetDir, $targetDir2); ?> copy and pasted from the doc.

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  • SQL Command Not Properly Ended (Nested Aggregation with Group-by)

    - by snowind
    I keep getting this error when I tried to execute this query, although I couldn't figure out what went wrong. I'm using Oracle and JDBC. Here's the query: SELECT Temp.flight_number, Temp.avgprice FROM (SELECT P.flight_number, AVG (P.amount) AS avgprice FROM purchase P GROUP BY P.flight_number) AS Temp WHERE Temp.avgprice = (SELECT MAX (Temp.avgprice) FROM Temp) I'm trying to get the maximum of average price of the tickets that customers have booked, group by flight_number.

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  • Ant command line arguments

    - by js7354
    Program works fine when run with eclipse run configurations, but when run with ant, it is unable to parse int from args[0], which I do not understand. Full code is available here https://gist.github.com/4108950/e984a581d5e9de889eaf0c8faf0e57752e825a97 I believe it has something to do with ant, target name="run" description="run the project"> java dir="${build.dir}" classname="BinarySearchTree" fork="yes"> <arg value="6 in.txt"/> /java> /target> the arg value will be changed via the -D flag, as in ant -Dargs="6 testData1.txt" run. Any help would be much appreciated, it is very frustrating.

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  • PHP shell command

    - by DGT
    Can anyone please tell me how to move file(s) into a dir in PHP? I did the following and it doesn't work. exec("temp/$file ../public/"); I would appreciate it.

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  • Understanding Service Compensation part of Industrial SOA series

    - by JuergenKress
    Some of the most important SOA design patterns that we have successfully applied in projects will be described in this article. These include the Compensation pattern and the UI mediator pattern, the Common Data Format pattern and the Data Access pattern. All of these patterns are included in Thomas Erl's book, "SOA Design Patterns", and are presented here in detail, together with our practical experiences. We begin our "best of" SOA pattern collection with the Compensation pattern. Compensation is required in error situations in an SOA, as multiple atomic service operations cannot generally be linked with classic transactions this would violate the principle of loose coupling. An error situation of this sort will occur, particularly if service operations are combined into processes or new services during orchestration or by applying the Composite pattern, and the transaction bracket has to be expanded as a result. We need mechanisms to undo the effects of individual services (the status changes in the overall system) and to ensure that a consistent system state is maintained at all times, so as to preserve system integrity. For the Compensation pattern, we would like to address the following questions: Why is compensation important in relation to SOA? How is the topic of compensation linked with the topic of transactions? What are the challenges with regard to compensation... Read the full article in the Service Technology Magazine or at OTN. Share your comments and feedback on the Industrial SOA series by using the hashtag #industrialsoa. Missed an article of the Industrial SOA series visit the overview at OTN. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Mix Forum Technorati Tags: Industrial SOA,SOA,SOA Service Compensation,Community,Oracle SOA,Oracle BPM,OPN,Jürgen Kress

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  • How to compile a C++ source code written for Linux/Unix on Windows Vista (code given)

    - by HTMZ
    I have a c++ source code that was written in linux/unix environment by some other author. It gives me errors when i compile it in windows vista environment. I am using Bloodshed Dev C++ v 4.9. please help. #include <iostream.h> #include <map> #include <vector> #include <string> #include <string.h> #include <strstream> #include <unistd.h> #include <stdlib.h> using namespace std; template <class T> class PrefixSpan { private: vector < vector <T> > transaction; vector < pair <T, unsigned int> > pattern; unsigned int minsup; unsigned int minpat; unsigned int maxpat; bool all; bool where; string delimiter; bool verbose; ostream *os; void report (vector <pair <unsigned int, int> > &projected) { if (minpat > pattern.size()) return; // print where & pattern if (where) { *os << "<pattern>" << endl; // what: if (all) { *os << "<freq>" << pattern[pattern.size()-1].second << "</freq>" << endl; *os << "<what>"; for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first; } else { *os << "<what>"; for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first << delimiter << pattern[i].second; } *os << "</what>" << endl; // where *os << "<where>"; for (unsigned int i = 0; i < projected.size(); i++) *os << (i ? " " : "") << projected[i].first; *os << "</where>" << endl; *os << "</pattern>" << endl; } else { // print found pattern only if (all) { *os << pattern[pattern.size()-1].second; for (unsigned int i = 0; i < pattern.size(); i++) *os << " " << pattern[i].first; } else { for (unsigned int i = 0; i < pattern.size(); i++) *os << (i ? " " : "") << pattern[i].first << delimiter << pattern[i].second; } *os << endl; } } void project (vector <pair <unsigned int, int> > &projected) { if (all) report(projected); map <T, vector <pair <unsigned int, int> > > counter; for (unsigned int i = 0; i < projected.size(); i++) { int pos = projected[i].second; unsigned int id = projected[i].first; unsigned int size = transaction[id].size(); map <T, int> tmp; for (unsigned int j = pos + 1; j < size; j++) { T item = transaction[id][j]; if (tmp.find (item) == tmp.end()) tmp[item] = j ; } for (map <T, int>::iterator k = tmp.begin(); k != tmp.end(); ++k) counter[k->first].push_back (make_pair <unsigned int, int> (id, k->second)); } for (map <T, vector <pair <unsigned int, int> > >::iterator l = counter.begin (); l != counter.end (); ) { if (l->second.size() < minsup) { map <T, vector <pair <unsigned int, int> > >::iterator tmp = l; tmp = l; ++tmp; counter.erase (l); l = tmp; } else { ++l; } } if (! all && counter.size () == 0) { report (projected); return; } for (map <T, vector <pair <unsigned int, int> > >::iterator l = counter.begin (); l != counter.end(); ++l) { if (pattern.size () < maxpat) { pattern.push_back (make_pair <T, unsigned int> (l->first, l->second.size())); project (l->second); pattern.erase (pattern.end()); } } } public: PrefixSpan (unsigned int _minsup = 1, unsigned int _minpat = 1, unsigned int _maxpat = 0xffffffff, bool _all = false, bool _where = false, string _delimiter = "/", bool _verbose = false): minsup(_minsup), minpat (_minpat), maxpat (_maxpat), all(_all), where(_where), delimiter (_delimiter), verbose (_verbose) {}; ~PrefixSpan () {}; istream& read (istream &is) { string line; vector <T> tmp; T item; while (getline (is, line)) { tmp.clear (); istrstream istrs ((char *)line.c_str()); while (istrs >> item) tmp.push_back (item); transaction.push_back (tmp); } return is; } ostream& run (ostream &_os) { os = &_os; if (verbose) *os << transaction.size() << endl; vector <pair <unsigned int, int> > root; for (unsigned int i = 0; i < transaction.size(); i++) root.push_back (make_pair (i, -1)); project (root); return *os; } void clear () { transaction.clear (); pattern.clear (); } }; int main (int argc, char **argv) { extern char *optarg; unsigned int minsup = 1; unsigned int minpat = 1; unsigned int maxpat = 0xffffffff; bool all = false; bool where = false; string delimiter = "/"; bool verbose = false; string type = "string"; int opt; while ((opt = getopt(argc, argv, "awvt:M:m:L:d:")) != -1) { switch(opt) { case 'a': all = true; break; case 'w': where = true; break; case 'v': verbose = true; break; case 'm': minsup = atoi (optarg); break; case 'M': minpat = atoi (optarg); break; case 'L': maxpat = atoi (optarg); break; case 't': type = string (optarg); break; case 'd': delimiter = string (optarg); break; default: cout << "Usage: " << argv[0] << " [-m minsup] [-M minpat] [-L maxpat] [-a] [-w] [-v] [-t type] [-d delimiter] < data .." << endl; return -1; } } if (type == "int") { PrefixSpan<unsigned int> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); }else if (type == "short") { PrefixSpan<unsigned short> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else if (type == "char") { PrefixSpan<unsigned char> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else if (type == "string") { PrefixSpan<string> prefixspan (minsup, minpat, maxpat, all, where, delimiter, verbose); prefixspan.read (cin); prefixspan.run (cout); } else { cerr << "Unknown Item Type: " << type << " : choose from [string|int|short|char]" << endl; return -1; } return 0; }

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  • Hard Disk DRDY error: is it a crash

    - by pranjal
    I am using IBM Thinkpad, 1.7GHz, 512 RAM with Linux Mint 9 installed. I have two partitions in addition to root. One of the partitions became read-only yesterday, after which I rebooted my system. It is extremely slow along with DRDY Error : Is my Hard disk crashed ? Error Log while booting. Differences between boot sector and its backup. failed command : READ DMA BMDMA : stat 0X25 ata 1.00 : status : { DRDY ERR } ata 1.00 : status :{ UNC } Buffer I/O error on logical device, logical block 65467 smartctl output for the partition: mint mint # smartctl -a /dev/sda1 smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen Home page is http://smartmontools.sourceforge.net/ === START OF INFORMATION SECTION === Device Model: TOSHIBA MK4026GAX RoHS Serial Number: X5LY1623T Firmware Version: PA107E User Capacity: 40,007,761,920 bytes Device is: Not in smartctl database [for details use: -P showall] ATA Version is: 6 ATA Standard is: Exact ATA specification draft version not indicated Local Time is: Thu Feb 17 06:48:25 2011 UTC SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === SMART overall-health self-assessment test result: PASSED General SMART Values: Offline data collection status: (0x84) Offline data collection activity was suspended by an interrupting command from host. Auto Offline Data Collection: Enabled. Self-test execution status: ( 0) The previous self-test routine completed without error or no self-test has ever been run. Total time to complete Offline data collection: ( 153) seconds. Offline data collection capabilities: (0x1b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. No Conveyance Self-test supported. No Selective Self-test supported. SMART capabilities: (0x0003) Saves SMART data before entering power-saving mode. Supports SMART auto save timer. Error logging capability: (0x01) Error logging supported. No General Purpose Logging support. Short self-test routine recommended polling time: ( 2) minutes. Extended self-test routine recommended polling time: ( 30) minutes. SMART Attributes Data Structure revision number: 16 Vendor Specific SMART Attributes with Thresholds: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000b 100 100 050 Pre-fail Always - 0 2 Throughput_Performance 0x0005 100 100 050 Pre-fail Offline - 0 3 Spin_Up_Time 0x0027 100 100 001 Pre-fail Always - 310 4 Start_Stop_Count 0x0032 100 100 000 Old_age Always - 3968 5 Reallocated_Sector_Ct 0x0033 100 100 050 Pre-fail Always - 40 7 Seek_Error_Rate 0x000b 100 100 050 Pre-fail Always - 0 8 Seek_Time_Performance 0x0005 100 100 050 Pre-fail Offline - 0 9 Power_On_Hours 0x0032 082 082 000 Old_age Always - 7257 10 Spin_Retry_Count 0x0033 179 100 030 Pre-fail Always - 0 12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 3484 192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 489 193 Load_Cycle_Count 0x0032 064 064 000 Old_age Always - 367150 194 Temperature_Celsius 0x0022 100 100 000 Old_age Always - 36 (Lifetime Min/Max 14/57) 196 Reallocated_Event_Count 0x0032 100 100 000 Old_age Always - 33 197 Current_Pending_Sector 0x0032 100 100 000 Old_age Always - 82 198 Offline_Uncorrectable 0x0030 100 100 000 Old_age Offline - 1 199 UDMA_CRC_Error_Count 0x0032 200 253 000 Old_age Always - 0 220 Disk_Shift 0x0002 100 100 000 Old_age Always - 101 222 Loaded_Hours 0x0032 085 085 000 Old_age Always - 6146 223 Load_Retry_Count 0x0032 100 100 000 Old_age Always - 0 224 Load_Friction 0x0022 100 100 000 Old_age Always - 0 226 Load-in_Time 0x0026 100 100 000 Old_age Always - 227 240 Head_Flying_Hours 0x0001 100 100 001 Pre-fail Offline - 0 SMART Error Log Version: 1 ATA Error Count: 2371 (device log contains only the most recent five errors) CR = Command Register [HEX] FR = Features Register [HEX] SC = Sector Count Register [HEX] SN = Sector Number Register [HEX] CL = Cylinder Low Register [HEX] CH = Cylinder High Register [HEX] DH = Device/Head Register [HEX] DC = Device Command Register [HEX] ER = Error register [HEX] ST = Status register [HEX] Powered_Up_Time is measured from power on, and printed as DDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes, SS=sec, and sss=millisec. It "wraps" after 49.710 days. Error 2371 occurred at disk power-on lifetime: 7256 hours (302 days + 8 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 05 1a 1b 00 e0 Error: UNC 5 sectors at LBA = 0x00001b1a = 6938 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 05 1a 1b 00 e0 00 00:03:10.061 READ DMA f8 00 00 00 00 00 e0 00 00:03:10.061 READ NATIVE MAX ADDRESS ec 00 00 00 00 00 a0 02 00:03:10.053 IDENTIFY DEVICE ef 03 45 00 00 00 a0 02 00:03:10.053 SET FEATURES [Set transfer mode] f8 00 00 00 00 00 e0 00 00:03:10.053 READ NATIVE MAX ADDRESS Error 2370 occurred at disk power-on lifetime: 7256 hours (302 days + 8 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 05 1a 1b 00 e0 Error: UNC 5 sectors at LBA = 0x00001b1a = 6938 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 05 1a 1b 00 e0 00 00:03:03.328 READ DMA f8 00 00 00 00 00 e0 00 00:03:03.327 READ NATIVE MAX ADDRESS ec 00 00 00 00 00 a0 02 00:03:03.320 IDENTIFY DEVICE ef 03 45 00 00 00 a0 02 00:03:03.319 SET FEATURES [Set transfer mode] f8 00 00 00 00 00 e0 00 00:03:03.319 READ NATIVE MAX ADDRESS Error 2369 occurred at disk power-on lifetime: 7256 hours (302 days + 8 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 05 1a 1b 00 e0 Error: UNC 5 sectors at LBA = 0x00001b1a = 6938 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 05 1a 1b 00 e0 00 00:02:56.582 READ DMA f8 00 00 00 00 00 e0 00 00:02:56.582 READ NATIVE MAX ADDRESS ec 00 00 00 00 00 a0 02 00:02:56.574 IDENTIFY DEVICE ef 03 45 00 00 00 a0 02 00:02:56.574 SET FEATURES [Set transfer mode] f8 00 00 00 00 00 e0 00 00:02:56.574 READ NATIVE MAX ADDRESS Error 2368 occurred at disk power-on lifetime: 7256 hours (302 days + 8 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 05 1a 1b 00 e0 Error: UNC 5 sectors at LBA = 0x00001b1a = 6938 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 05 1a 1b 00 e0 00 00:02:49.809 READ DMA f8 00 00 00 00 00 e0 00 00:02:49.809 READ NATIVE MAX ADDRESS ec 00 00 00 00 00 a0 02 00:02:49.801 IDENTIFY DEVICE ef 03 45 00 00 00 a0 02 00:02:49.801 SET FEATURES [Set transfer mode] f8 00 00 00 00 00 e0 00 00:02:49.801 READ NATIVE MAX ADDRESS Error 2367 occurred at disk power-on lifetime: 7256 hours (302 days + 8 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 05 1a 1b 00 e0 Error: UNC 5 sectors at LBA = 0x00001b1a = 6938 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 05 1a 1b 00 e0 00 00:02:43.056 READ DMA f8 00 00 00 00 00 e0 00 00:02:43.056 READ NATIVE MAX ADDRESS ec 00 00 00 00 00 a0 02 00:02:43.048 IDENTIFY DEVICE ef 03 45 00 00 00 a0 02 00:02:43.048 SET FEATURES [Set transfer mode] f8 00 00 00 00 00 e0 00 00:02:43.047 READ NATIVE MAX ADDRESS SMART Self-test log structure revision number 1 No self-tests have been logged. [To run self-tests, use: smartctl -t] Device does not support Selective Self Tests/Logging Do I need to get a new Hard Disk my PC ?

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  • Azure &ndash; Part 5 &ndash; Repository Pattern for Table Service

    - by Shaun
    In my last post I created a very simple WCF service with the user registration functionality. I created an entity for the user data and a DataContext class which provides some methods for operating the entities such as add, delete, etc. And in the service method I utilized it to add a new entity into the table service. But I didn’t have any validation before registering which is not acceptable in a real project. So in this post I would firstly add some validation before perform the data creation code and show how to use the LINQ for the table service.   LINQ to Table Service Since the table service utilizes ADO.NET Data Service to expose the data and the managed library of ADO.NET Data Service supports LINQ we can use it to deal with the data of the table service. Let me explain with my current example: I would like to ensure that when register a new user the email address should be unique. So I need to check the account entities in the table service before add. If you remembered, in my last post I mentioned that there’s a method in the TableServiceContext class – CreateQuery, which will create a IQueryable instance from a given type of entity. So here I would create a method under my AccountDataContext class to return the IQueryable<Account> which named Load. 1: public class AccountDataContext : TableServiceContext 2: { 3: private CloudStorageAccount _storageAccount; 4:  5: public AccountDataContext(CloudStorageAccount storageAccount) 6: : base(storageAccount.TableEndpoint.AbsoluteUri, storageAccount.Credentials) 7: { 8: _storageAccount = storageAccount; 9:  10: var tableStorage = new CloudTableClient(_storageAccount.TableEndpoint.AbsoluteUri, 11: _storageAccount.Credentials); 12: tableStorage.CreateTableIfNotExist("Account"); 13: } 14:  15: public void Add(Account accountToAdd) 16: { 17: AddObject("Account", accountToAdd); 18: SaveChanges(); 19: } 20:  21: public IQueryable<Account> Load() 22: { 23: return CreateQuery<Account>("Account"); 24: } 25: } The method returns the IQueryable<Account> so that I can perform the LINQ operation on it. And back to my service class, I will use it to implement my validation. 1: public bool Register(string email, string password) 2: { 3: var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString"); 4: var accountToAdd = new Account(email, password) { DateCreated = DateTime.Now }; 5: var accountContext = new AccountDataContext(storageAccount); 6:  7: // validation 8: var accountNumber = accountContext.Load() 9: .Where(a => a.Email == accountToAdd.Email) 10: .Count(); 11: if (accountNumber > 0) 12: { 13: throw new ApplicationException(string.Format("Your account {0} had been used.", accountToAdd.Email)); 14: } 15:  16: // create entity 17: try 18: { 19: accountContext.Add(accountToAdd); 20: return true; 21: } 22: catch (Exception ex) 23: { 24: Trace.TraceInformation(ex.ToString()); 25: } 26: return false; 27: } I used the Load method to retrieve the IQueryable<Account> and use Where method to find the accounts those email address are the same as the one is being registered. If it has I through an exception back to the client side. Let’s run it and test from my simple client application. Oops! Looks like we encountered an unexpected exception. It said the “Count” is not support by the ADO.NET Data Service LINQ managed library. That is because the table storage managed library (aka. TableServiceContext) is based on the ADO.NET Data Service and it supports very limit LINQ operation. Although I didn’t find a full list or documentation about which LINQ methods it supports I could even refer a page on msdn here. It gives us a roughly summary of which query operation the ADO.NET Data Service managed library supports and which doesn't. As you see the Count method is not in the supported list. Not only the query operation, there inner lambda expression in the Where method are limited when using the ADO.NET Data Service managed library as well. For example if you added (a => !a.DateDeleted.HasValue) in the Where method to exclude those deleted account it will raised an exception said "Invalid Input". Based on my experience you should always use the simple comparison (such as ==, >, <=, etc.) on the simple members (such as string, integer, etc.) and do not use any shortcut methods (such as string.Compare, string.IsNullOrEmpty etc.). 1: // validation 2: var accountNumber = accountContext.Load() 3: .Where(a => a.Email == accountToAdd.Email) 4: .ToList() 5: .Count; 6: if (accountNumber > 0) 7: { 8: throw new ApplicationException(string.Format("Your account {0} had been used.", accountToAdd.Email)); 9: } We changed the a bit and try again. Since I had created an account with my mail address so this time it gave me an exception said that the email had been used, which is correct.   Repository Pattern for Table Service The AccountDataContext takes the responsibility to save and load the account entity but only for that specific entity. Is that possible to have a dynamic or generic DataContext class which can operate any kinds of entity in my system? Of course yes. Although there's no typical database in table service we can threat the entities as the records, similar with the data entities if we used OR Mapping. As we can use some patterns for ORM architecture here we should be able to adopt the one of them - Repository Pattern in this example. We know that the base class - TableServiceContext provide 4 methods for operating the table entities which are CreateQuery, AddObject, UpdateObject and DeleteObject. And we can create a relationship between the enmity class, the table container name and entity set name. So it's really simple to have a generic base class for any kinds of entities. Let's rename the AccountDataContext to DynamicDataContext and make the type of Account as a type parameter if it. 1: public class DynamicDataContext<T> : TableServiceContext where T : TableServiceEntity 2: { 3: private CloudStorageAccount _storageAccount; 4: private string _entitySetName; 5:  6: public DynamicDataContext(CloudStorageAccount storageAccount) 7: : base(storageAccount.TableEndpoint.AbsoluteUri, storageAccount.Credentials) 8: { 9: _storageAccount = storageAccount; 10: _entitySetName = typeof(T).Name; 11:  12: var tableStorage = new CloudTableClient(_storageAccount.TableEndpoint.AbsoluteUri, 13: _storageAccount.Credentials); 14: tableStorage.CreateTableIfNotExist(_entitySetName); 15: } 16:  17: public void Add(T entityToAdd) 18: { 19: AddObject(_entitySetName, entityToAdd); 20: SaveChanges(); 21: } 22:  23: public void Update(T entityToUpdate) 24: { 25: UpdateObject(entityToUpdate); 26: SaveChanges(); 27: } 28:  29: public void Delete(T entityToDelete) 30: { 31: DeleteObject(entityToDelete); 32: SaveChanges(); 33: } 34:  35: public IQueryable<T> Load() 36: { 37: return CreateQuery<T>(_entitySetName); 38: } 39: } I saved the name of the entity type when constructed for performance matter. The table name, entity set name would be the same as the name of the entity class. The Load method returned a generic IQueryable instance which supports the lazy load feature. Then in my service class I changed the AccountDataContext to DynamicDataContext and that's all. 1: var accountContext = new DynamicDataContext<Account>(storageAccount); Run it again and register another account. The DynamicDataContext now can be used for any entities. For example, I would like the account has a list of notes which contains 3 custom properties: Account Email, Title and Content. We create the note entity class. 1: public class Note : TableServiceEntity 2: { 3: public string AccountEmail { get; set; } 4: public string Title { get; set; } 5: public string Content { get; set; } 6: public DateTime DateCreated { get; set; } 7: public DateTime? DateDeleted { get; set; } 8:  9: public Note() 10: : base() 11: { 12: } 13:  14: public Note(string email) 15: : base(email, string.Format("{0}_{1}", email, Guid.NewGuid().ToString())) 16: { 17: AccountEmail = email; 18: } 19: } And no need to tweak the DynamicDataContext we can directly go to the service class to implement the logic. Notice here I utilized two DynamicDataContext instances with the different type parameters: Note and Account. 1: public class NoteService : INoteService 2: { 3: public void Create(string email, string title, string content) 4: { 5: var storageAccount = CloudStorageAccount.FromConfigurationSetting("DataConnectionString"); 6: var accountContext = new DynamicDataContext<Account>(storageAccount); 7: var noteContext = new DynamicDataContext<Note>(storageAccount); 8:  9: // validate - email must be existed 10: var accounts = accountContext.Load() 11: .Where(a => a.Email == email) 12: .ToList() 13: .Count; 14: if (accounts <= 0) 15: throw new ApplicationException(string.Format("The account {0} does not exsit in the system please register and try again.", email)); 16:  17: // save the note 18: var noteToAdd = new Note(email) { Title = title, Content = content, DateCreated = DateTime.Now }; 19: noteContext.Add(noteToAdd); 20: } 21: } And updated our client application to test the service. I didn't implement any list service to show all notes but we can have a look on the local SQL database if we ran it at local development fabric.   Summary In this post I explained a bit about the limited LINQ support for the table service. And then I demonstrated about how to use the repository pattern in the table service data access layer and make the DataContext dynamically. The DynamicDataContext I created in this post is just a prototype. In fact we should create the relevant interface to make it testable and for better structure we'd better separate the DataContext classes for each individual kind of entity. So it should have IDataContextBase<T>, DataContextBase<T> and for each entity we would have class AccountDataContext<Account> : IDataContextBase<Account>, DataContextBase<Account> { … } class NoteDataContext<Note> : IDataContextBase<Note>, DataContextBase<Note> { … }   Besides the structured data saving and loading, another common scenario would be saving and loading some binary data such as images, files. In my next post I will show how to use the Blob Service to store the bindery data - make the account be able to upload their logo in my example.   Hope this helps, Shaun   All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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  • git post-receive hook throws "command not found" error but seems to run properly and no errors when run manually

    - by Ben
    I have a post-receive hook that runs on a central git repository set up with gitolite to trigger a git pull on a staging server. It seems to work properly, but throws a "command not found" error when it is run. I am trying to track down the source of the error, but have not had any luck. Running the same commands manually does not produce an error. The error changes depending on what was done in the commit that is being pushed to the central repository. For instance, if 'git rm ' was committed and pushed to the central repo the error message will be "remote: hooks/post-receive: line 16: Removed: command not found" and if 'git add ' was committed and pushed to the central repo the error message will be "remote: hooks/post-receive: line 16: Merge: command not found". In either case the 'git pull' run on the staging server works correctly despite the error message. Here is the post-receive script: #!/bin/bash # # This script is triggered by a push to the local git repository. It will # ssh into a remote server and perform a git pull. # # The SSH_USER must be able to log into the remote server with a # passphrase-less SSH key *AND* be able to do a git pull without a passphrase. # # The command to actually perform the pull request on the remost server comes # from the ~/.ssh/authorized_keys file on the REMOTE_HOST and is triggered # by the ssh login. SSH_USER="remoteuser" REMOTE_HOST="staging.server.com" `ssh $SSH_USER@$REMOTE_HOST` # This is line 16 echo "Done!" The command that does the git pull on the staging server is in the ssh user's ~/.ssh/authorized_keys file and is: command="cd /var/www/staging_site; git pull",no-port-forwarding,no-X11-forwarding,no-agent-forwarding, ssh-rsa AAAAB3NzaC1yc2EAAAABIwAA... (the rest of the public key) This is the actual output from removing a file from my local repo, committing it locally, and pushing it to the central git repo: ben@tamarack:~/thejibe/testing/web$ git rm ./testing rm 'testing' ben@tamarack:~/thejibe/testing/web$ git commit -a -m "Remove testing file" [master bb96e13] Remove testing file 1 files changed, 0 insertions(+), 5 deletions(-) delete mode 100644 testing ben@tamarack:~/thejibe/testing/web$ git push Counting objects: 3, done. Delta compression using up to 2 threads. Compressing objects: 100% (2/2), done. Writing objects: 100% (2/2), 221 bytes, done. Total 2 (delta 1), reused 0 (delta 0) remote: From [email protected]:testing remote: aa72ad9..bb96e13 master -> origin/master remote: hooks/post-receive: line 16: Removed: command not found # The error msg remote: Done! To [email protected]:testing aa72ad9..bb96e13 master -> master ben@tamarack:~/thejibe/testing/web$ As you can see the post-receive script gets to the echo "Done!" line and when I look on the staging server the git pull has been successfully run, but there's still that nagging error message. Any suggestions on where to look for the source of the error message would be greatly appreciated. I'm tempted to redirect stderr to /dev/null but would prefer to know what the problem is.

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  • git post-receive hook throws "command not found" error but seems to run properly and no errors when run manually

    - by Ben
    I have a post-receive hook that runs on a central git repository set up with gitolite to trigger a git pull on a staging server. It seems to work properly, but throws a "command not found" error when it is run. I am trying to track down the source of the error, but have not had any luck. Running the same commands manually does not produce an error. The error changes depending on what was done in the commit that is being pushed to the central repository. For instance, if 'git rm ' was committed and pushed to the central repo the error message will be "remote: hooks/post-receive: line 16: Removed: command not found" and if 'git add ' was committed and pushed to the central repo the error message will be "remote: hooks/post-receive: line 16: Merge: command not found". In either case the 'git pull' run on the staging server works correctly despite the error message. Here is the post-receive script: #!/bin/bash # # This script is triggered by a push to the local git repository. It will # ssh into a remote server and perform a git pull. # # The SSH_USER must be able to log into the remote server with a # passphrase-less SSH key *AND* be able to do a git pull without a passphrase. # # The command to actually perform the pull request on the remost server comes # from the ~/.ssh/authorized_keys file on the REMOTE_HOST and is triggered # by the ssh login. SSH_USER="remoteuser" REMOTE_HOST="staging.server.com" `ssh $SSH_USER@$REMOTE_HOST` # This is line 16 echo "Done!" The command that does the git pull on the staging server is in the ssh user's ~/.ssh/authorized_keys file and is: command="cd /var/www/staging_site; git pull",no-port-forwarding,no-X11-forwarding,no-agent-forwarding, ssh-rsa AAAAB3NzaC1yc2EAAAABIwAA... (the rest of the public key) This is the actual output from removing a file from my local repo, committing it locally, and pushing it to the central git repo: ben@tamarack:~/thejibe/testing/web$ git rm ./testing rm 'testing' ben@tamarack:~/thejibe/testing/web$ git commit -a -m "Remove testing file" [master bb96e13] Remove testing file 1 files changed, 0 insertions(+), 5 deletions(-) delete mode 100644 testing ben@tamarack:~/thejibe/testing/web$ git push Counting objects: 3, done. Delta compression using up to 2 threads. Compressing objects: 100% (2/2), done. Writing objects: 100% (2/2), 221 bytes, done. Total 2 (delta 1), reused 0 (delta 0) remote: From [email protected]:testing remote: aa72ad9..bb96e13 master -> origin/master remote: hooks/post-receive: line 16: Removed: command not found # The error msg remote: Done! To [email protected]:testing aa72ad9..bb96e13 master -> master ben@tamarack:~/thejibe/testing/web$ As you can see the post-receive script gets to the echo "Done!" line and when I look on the staging server the git pull has been successfully run, but there's still that nagging error message. Any suggestions on where to look for the source of the error message would be greatly appreciated. I'm tempted to redirect stderr to /dev/null but would prefer to know what the problem is.

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  • Why is this exception thrown when trying to match this regex in Java?

    - by Scott Ferguson
    I'm trying to match a specific string out of a an HTML document and have this regex pattern to grab it: Pattern somePattern = Pattern.compile("var json = ({\"r\":\"^d1\".*});"); However when I try to hit that code at runtime, I get this error: FATAL EXCEPTION: Timer-0 java.util.regex.PatternSyntaxException: Syntax error U_REGEX_RULE_SYNTAX near index 13: var json = ({"r":"^d1".*}); ^ at com.ibm.icu4jni.regex.NativeRegEx.open(Native Method) at java.util.regex.Pattern.compileImpl(Pattern.java:383) at java.util.regex.Pattern.<init>(Pattern.java:341) at java.util.regex.Pattern.compile(Pattern.java:317) Can anybody tell me what I'm doing wrong?

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  • Auto not being recognised by the compiler, what would be the best replacement?

    - by user1719605
    So I have wrote a program that uses auto however the compiler doesn't seem to recognize it, probably it is an earlier compiler. I was wondering for my code, with are suitable variables to fix my code so that I do not need to use the auto keyword? I'm thinking a pointer to a string? or a string iterator, though I am not sure. #include <cstdlib> #include <string> #include <iostream> #include <unistd.h> #include <algorithm> using namespace std; int main(int argc, char* argv[]) { enum MODE { WHOLE, PREFIX, SUFFIX, ANYWHERE, EMBEDDED } mode = WHOLE; bool reverse_match = false; int c; while ((c = getopt(argc, argv, ":wpsaev")) != -1) { switch (c) { case 'w': // pattern matches whole word mode = WHOLE; break; case 'p': // pattern matches prefix mode = PREFIX; break; case 'a': // pattern matches anywhere mode = ANYWHERE; break; case 's': // pattern matches suffix mode = SUFFIX; break; case 'e': // pattern matches anywhere mode = EMBEDDED; break; case 'v': // reverse sense of match reverse_match = true; break; } } argc -= optind; argv += optind; string pattern = argv[0]; string word; int matches = 0; while (cin >> word) { switch (mode) { case WHOLE: if (reverse_match) { if (pattern != word) { matches += 1; cout << word << endl; } } else if (pattern == word) { matches += 1; cout << word << endl; } break; case PREFIX: if (pattern.size() <= word.size()) { auto res = mismatch(pattern.begin(), pattern.end(), word.begin()); if (reverse_match) { if (res.first != word.end()) { matches += 1; cout << word << endl; } } else if (res.first == word.end()) { matches += 1; cout << word << endl; } } break; case ANYWHERE: if (reverse_match) { if (!word.find(pattern) != string::npos) { matches += 1; cout << word << endl; } } else if (word.find(pattern) != string::npos) { matches += 1; cout << word << endl; } break; case SUFFIX: if (pattern.size() <= word.size()) { auto res = mismatch(pattern.rbegin(), pattern.rend(), word.rbegin()); if (reverse_match) { if (res.first != word.rend()) { matches = +1; cout << word << endl; } } else if (res.first == word.rend()) { matches = +1; cout << word << endl; } } break; case EMBEDDED: if (reverse_match) { if (!pattern.find(word) != string::npos) { matches += 1; cout << word << endl;} } else if (pattern.find(word) != string::npos) { matches += 1; cout << word << endl; } break; } } return (matches == 0) ? 1 : 0; } Thanks in advance!

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  • Expert F# &ndash; Pattern Matching with Adam and Eve

    - by MarkPearl
    So I am loving my Expert F# book. I wish I had more time with it, but the little time I get I really enjoy. However today I was completely stumped by what the book was trying to get across with regards to pattern matching. On Page 38 – Chapter 3, it briefly describes F# option values. On this page it gives the code snippet along the code lines below and then goes on to speak briefly about pattern matching... open System type 'a option = | None | Some of 'a let people = [ ("Adam", None); ("Eve", None); ("Cain", Some("Adam", "Eve")); ("Abel", Some("Adam", "Eve")) ] let showParents(name, parents) = match parents with | Some(dad, mum) -> printfn "%s has father %s, mother %s" name dad mum | None -> printfn "%s has no parents!" name Console.WriteLine(showParents("Adam", None))   Originally when I read this code I think I misunderstood the purpose of the example code. I for some reason thought that the showParents function would magically be parsing the people array and looking for a match of name and then showing the parents. But obviously it cannot do this since there is no reference to the people array in the showParents method. After rereading the page I realized that I had just combined the two segments of code together, possibly incorrectly, and that a better example would have been to have a code snippet like the following. let showParents(name, parents) = match parents with | Some(dad, mum) -> printfn "%s has father %s, mother %s" name dad mum | None -> printfn "%s has no parents!" name Console.WriteLine(showParents("Adam", None)) Console.WriteLine(showParents("Cain", Some("Adam", "Eve"))) Console.ReadLine()   However, what if I wanted to have a function that was passed a list of people and a name would then show the parents of the name if there were any, and if not would show that they had no parents… so that doesnt seem to difficult does it… lets look at my very unoptimized noob F# code to try and achieve this… open System let people = [ ("Adam", None); ("Eve", None); ("Cain", Some("Adam", "Eve")); ("Abel", Some("Adam", "Eve")) ] // // returns the name of the person // let showName(person : string * (string * string) option) = let name = fst(person) name // // Returns a string with the parents details or not // let showParents(itemData : string * (string * string) option) = let name = fst(itemData) let parents = snd(itemData) match parents with | Some(dad, mum) -> "Father " + dad + " and Mother " + mum | None -> "Has no parents!" // // Prints the details // let showDetails(person : string * (string * string) option) = Console.WriteLine(showName(person)) Console.WriteLine(showParents(person)) // // Check if the name matches the first portion of person // if so, return true, else return false // let nameMatch(name : string , person : string * (string * string) option) = match name with | x when x = fst(person) -> true | _ -> false // // Searches an array of people and looks for a match of names // let findPerson(name : string, people : (string * (string * string) option) list) = let o = Seq.tryFind(fun x -> nameMatch(name, x)) people if Option.isSome o then o else Option.None // // Try and find a person, if found show their details // else show no match // let FoundPerson = findPerson("Cain", people) match FoundPerson with | None -> Console.WriteLine("Not found") | Some(x) -> showDetails(x) Console.ReadLine() So, my code isn’t the cleanest but it did teach me a bit more F#. The area that I learnt about was the option keyword. The challenge being, if a match of the name isn’t found – and if a name is found but the person doesn’t have parents it should react accordingly. I’m pretty sure I can optimize this code quite a bit more and I think I may come back to it sometime in the future and relook at it, but for now at least I was able to achieve what I wanted.. and my brain has gone just that wee little bit more functional.

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  • When trying to install Wine on 12.10, 'Sudo' command will not let me type in a password.

    - by Nocturnus
    As the title explains, I have been attempting to install Wine on my laptop which is running 12.10. When I access the command terminal and entered "sudo add-apt-repository ppa:ubuntu-wine/ppa" I was of course met by a password block, when I attempted to enter my password, it flat out wouldn't let me type anything, the only key that got a response from the terminal was "enter" which was met by "incorrect password". To bypass this issue I backed out and used the 'Gksudo' command, this new dialogue box seemed to give me access to sudo commands. I then entered "sudo apt-get update" and "sudo apt-get install wine1.5". Up until the installation everything went fine, but after entering the final command (still using gksudo) The terminal read "the following packages have unmet dependencies" and proceeded to list a bunch of "recommends" So my guess is that Wine hasn't been updated to run on 12.10... Is this true, and is there any other way to open .exe's? Also what was with that funky password misshap? I'm totally new to Ubuntu so I've just been using support pages and tutorials, sorry if I'm a bit naive in these matters...

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  • Nginx rewrites - When does one use the break flag (pattern target break)?

    - by anonymous-one
    The nginx wiki states: break - completes processing of current rewrite directives and non-rewrite processing continues within the current location block only. Is this to say that: If the rewrite pattern matches, process the rewrite (rewrite to target) but do not process any of the other rules in the location block, and process all other (cache, proxy, etc) directives in the location block? I am talking about the break flag as per: PATTERN TARGET FLAG Not the "break;" directive. Thanks.

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  • How do I execute a shell-command in background?

    - by Adobe
    Here's a simple defun to run a shell script: (defun bk-konsoles () "Calls: bk-konsoles.bash" (interactive) (shell-command (concat (expand-file-name "~/its/plts/goodies/bk-konsoles.bash ") (if (buffer-file-name) (file-name-directory (buffer-file-name))) " &") nil nil)) If I start a program with no ampersand - it start the script, but blocks emacs until I close the program, if I don't put ampersand it gives error: /home/boris/its/plts/goodies/bk-konsoles.bash /home/boris/scl/geekgeek/: exited abnormally with code 1. Edit: So now I'm using: (defun bk-konsoles () "Calls: bk-konsoles.bash" (interactive) (shell-command (concat (expand-file-name "~/its/plts/goodies/bk-konsoles.bash ") (if (buffer-file-name) (file-name-directory (buffer-file-name))) " & disown") nil nil) (kill-buffer "*Shell Command Output*")) Edit 2: Nope - doesn't work: (defun bk-konsoles () "Calls: bk-konsoles.bash" (interactive) (let ((curDir default-directory)) ;; (shell-command (concat "nohup " (expand-file-name "~/its/plts/goodies/bk-konsoles.bash ") curDir) nil nil) (shell-command (concat (expand-file-name "~/its/plts/goodies/bk-konsoles.bash ") curDir "& disown") nil nil) (kill-buffer "*Shell Command Output*"))) keeps emacs busy - either with disown, or nohup. Here's a script I'm running if it might be of help: bk-konsoles.bash

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  • Essential AIML responses?

    - by user335932
    What do you think are important pattern/temples to program. Like in a chatbot what does EVERY chatbot need a response for? Im just starting out making the aiml file and need some help... Heres the file now. <aiml> <category> <pattern>Hey</pattern> <template>Whats up?</template> <category> <category> <pattern>WHAT ARE YOU?</pattern> <template>I am a chatbot.</template> <category> <category> <pattern>DO YOU LIKE*</pattern> <template>Yes, I love <star/></template> <category> <category> <pattern>WHAT IS*</pattern> <template><star/>? is that what humans call what I did to your mom last night?</template> <category> <category> <pattern>WHEN WERE YOUR BORN*</pattern> <template>I was created in 2010.</template> <category>

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  • I need to remove Java Script tags using regular expressions and JRegex

    - by piotr
    I need to remove all the Java Script tags and the content in between and style tags from the HTML code of web pages.So far I've come up with this expression : "(<[ \r\n\t]script([ \r\n\t]|){1,}([ \r\n\t]|.)?)|(<[ \r\n\t]noscript([ \r\n\t]|){1,}([ \r\n\t]|.)?)|(<[ \r\n\t]style([ \r\n\t]|){1,}([ \r\n\t]|.)?)" I use JRegex library to work with regular expressions. When I test it in any regex tester it works just fine, but once I run my program - it all crashes down with this error report: Exception in thread "Thread-0" java.lang.StackOverflowError at java.util.regex.Pattern$BranchConn.match(Unknown Source) at java.util.regex.Pattern$BmpCharProperty.match(Unknown Source) at java.util.regex.Pattern$Branch.match(Unknown Source) at java.util.regex.Pattern$GroupHead.match(Unknown Source) at java.util.regex.Pattern$LazyLoop.match(Unknown Source) at java.util.regex.Pattern$GroupTail.match(Unknown Source) at java.util.regex.Pattern$BranchConn.match(Unknown Source) at java.util.regex.Pattern$CharProperty.match(Unknown Source) at java.util.regex.Pattern$Branch.match(Unknown Source) at java.util.regex.Pattern$GroupHead.match(Unknown Source) at java.util.regex.Pattern$LazyLoop.match(Unknown Source) .................................. And it keeps on going forever. If anyone can give me an advice on this one - I'll be very grateful.

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  • C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

    - by James Michael Hare
    So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton, the basic Design Pattern is that a Singleton class is one where there is only ever one instance of the class created.  This means that constructors must be private to avoid users creating their own instances, and a static property (or method in languages without properties) is defined that returns a single static instance. 1: public class Singleton 2: { 3: // the single instance is defined in a static field 4: private static readonly Singleton _instance = new Singleton(); 5:  6: // constructor private so users can't instantiate on their own 7: private Singleton() 8: { 9: } 10:  11: // read-only property that returns the static field 12: public static Singleton Instance 13: { 14: get 15: { 16: return _instance; 17: } 18: } 19: } This is the most basic singleton, notice the key features: Static readonly field that contains the one and only instance. Constructor is private so it can only be called by the class itself. Static property that returns the single instance. Looks like it satisfies, right?  There's just one (potential) problem.  C# gives you no guarantee of when the static field _instance will be created.  This is because the C# standard simply states that classes (which are marked in the IL as BeforeFieldInit) can have their static fields initialized any time before the field is accessed.  This means that they may be initialized on first use, they may be initialized at some other time before, you can't be sure when. So what if you want to guarantee your instance is truly lazy.  That is, that it is only created on first call to Instance?  Well, there's a few ways to do this.  First we'll show the old ways, and then talk about how .Net 4.0's new System.Lazy<T> type can help make the lazy-Singleton cleaner. Obviously, we could take on the lazy construction ourselves, but being that our Singleton may be accessed by many different threads, we'd need to lock it down. 1: public class LazySingleton1 2: { 3: // lock for thread-safety laziness 4: private static readonly object _mutex = new object(); 5:  6: // static field to hold single instance 7: private static LazySingleton1 _instance = null; 8:  9: // property that does some locking and then creates on first call 10: public static LazySingleton1 Instance 11: { 12: get 13: { 14: if (_instance == null) 15: { 16: lock (_mutex) 17: { 18: if (_instance == null) 19: { 20: _instance = new LazySingleton1(); 21: } 22: } 23: } 24:  25: return _instance; 26: } 27: } 28:  29: private LazySingleton1() 30: { 31: } 32: } This is a standard double-check algorithm so that you don't lock if the instance has already been created.  However, because it's possible two threads can go through the first if at the same time the first time back in, you need to check again after the lock is acquired to avoid creating two instances. Pretty straightforward, but ugly as all heck.  Well, you could also take advantage of the C# standard's BeforeFieldInit and define your class with a static constructor.  It need not have a body, just the presence of the static constructor will remove the BeforeFieldInit attribute on the class and guarantee that no fields are initialized until the first static field, property, or method is called.   1: public class LazySingleton2 2: { 3: // because of the static constructor, this won't get created until first use 4: private static readonly LazySingleton2 _instance = new LazySingleton2(); 5:  6: // Returns the singleton instance using lazy-instantiation 7: public static LazySingleton2 Instance 8: { 9: get { return _instance; } 10: } 11:  12: // private to prevent direct instantiation 13: private LazySingleton2() 14: { 15: } 16:  17: // removes BeforeFieldInit on class so static fields not 18: // initialized before they are used 19: static LazySingleton2() 20: { 21: } 22: } Now, while this works perfectly, I hate it.  Why?  Because it's relying on a non-obvious trick of the IL to guarantee laziness.  Just looking at this code, you'd have no idea that it's doing what it's doing.  Worse yet, you may decide that the empty static constructor serves no purpose and delete it (which removes your lazy guarantee).  Worse-worse yet, they may alter the rules around BeforeFieldInit in the future which could change this. So, what do I propose instead?  .Net 4.0 adds the System.Lazy type which guarantees thread-safe lazy-construction.  Using System.Lazy<T>, we get: 1: public class LazySingleton3 2: { 3: // static holder for instance, need to use lambda to construct since constructor private 4: private static readonly Lazy<LazySingleton3> _instance 5: = new Lazy<LazySingleton3>(() => new LazySingleton3()); 6:  7: // private to prevent direct instantiation. 8: private LazySingleton3() 9: { 10: } 11:  12: // accessor for instance 13: public static LazySingleton3 Instance 14: { 15: get 16: { 17: return _instance.Value; 18: } 19: } 20: } Note, you need your lambda to call the private constructor as Lazy's default constructor can only call public constructors of the type passed in (which we can't have by definition of a Singleton).  But, because the lambda is defined inside our type, it has access to the private members so it's perfect. Note how the Lazy<T> makes it obvious what you're doing (lazy construction), instead of relying on an IL generation side-effect.  This way, it's more maintainable.  Lazy<T> has many other uses as well, obviously, but I really love how elegant and readable it makes the lazy Singleton.

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  • When modeling a virtual circuit board, what is the best design pattern to check for cycles?

    - by Wallace Brown
    To make it simple assume you have only AND and OR gates. Each has two inputs and one output. The output of two inputs can be used as an input for the next gate For example: A AND B - E C AND D - F E OR F - G Assuming an arbitrary number of gates, we want to check if the circuit ever connects back into itself at an earlier state? For example: E AND F - A This should be illegal since it creates an endless cycle. What design pattern would best be able to check for these cycles?

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  • Is loose coupling w/o use cases an anti-pattern?

    - by dsimcha
    Loose coupling is, to some developers, the holy grail of well-engineered software. It's certainly a good thing when it makes code more flexible in the face of changes that are likely to occur in the foreseeable future, or avoids code duplication. On the other hand, efforts to loosely couple components increase the amount of indirection in a program, thus increasing its complexity, often making it more difficult to understand and often making it less efficient. Do you consider a focus on loose coupling without any use cases for the loose coupling (such as avoiding code duplication or planning for changes that are likely to occur in the foreseeable future) to be an anti-pattern? Can loose coupling fall under the umbrella of YAGNI?

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