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Ideas Related to Subset Sum with 2,3 and more integers

- by rolandbishop

I've been struggling with this problem just like everyone else and I'm quite sure there has been more than enough posts to explain this problem. However in terms of understanding it fully, I wanted to share my thoughts and get more efficient solutions from all the great people in here related to Subset Sum problem. I've searched it over the Internet and there is actually a lot sources but I'm really willing to re-implement an algorithm or finding my own in order to understand fully. The key thing I'm struggling with is the efficiency considering the set size will be large. (I do not have a limit, just conceptually large). The two phases I'm trying to implement ideas on is finding two numbers that are equal to given integer T, finding three numbers and eventually K numbers. Some ideas I've though; For the two integer part I'm thing basically sorting the array O(nlogn) and for each element in the array searching for its negative value. (i.e if the array element is 3 searching for -3). Maybe a hash table inclusion could be better, providing a O(1) indexing the element? For the three or more integers I've found an amazing blog post;http://www.skorks.com/2011/02/algorithms-a-dropbox-challenge-and-dynamic-programming/. However even the author itself states that it is not applicable for large numbers. So I was for 2 and 3 and more integers what ideas could be applied for the subset problem. I'm struggling with setting up a dynamic programming method that will be efficient for the large inputs as well.

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Asp.net membership salt?

- by chobo2

Hi Does anyone know how Asp.net membership generates their salt key and then how they encode it(ie is it salt + password or password + salt)? I am using sha1 with my membership but I would like to recreate the same salts so the built in membership stuff could hash the stuff the same way as my stuff can. Thanks Edit 2 Never Mind I mis read it and was thinking it said bytes not bit. So I was passing in 128 bytes not 128bits. Edit I been trying to make it so this is what I have public string EncodePassword(string password, string salt) { byte[] bytes = Encoding.Unicode.GetBytes(password); byte[] src = Encoding.Unicode.GetBytes(salt); byte[] dst = new byte[src.Length + bytes.Length]; Buffer.BlockCopy(src, 0, dst, 0, src.Length); Buffer.BlockCopy(bytes, 0, dst, src.Length, bytes.Length); HashAlgorithm algorithm = HashAlgorithm.Create("SHA1"); byte[] inArray = algorithm.ComputeHash(dst); return Convert.ToBase64String(inArray); } private byte[] createSalt(byte[] saltSize) { byte[] saltBytes = saltSize; RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetNonZeroBytes(saltBytes); return saltBytes; } So I have not tried to see if the asp.net membership will recognize this yet the hashed password looks close. I just don't know how to convert it to base64 for the salt. I did this byte[] storeSalt = createSalt(new byte[128]); string salt = Encoding.Unicode.GetString(storeSalt); string base64Salt = Convert.ToBase64String(storeSalt); int test = base64Salt.Length; Test length is 172 what is well over the 128bits so what am I doing wrong? This is what their salt looks like vkNj4EvbEPbk1HHW+K8y/A== This is what my salt looks like E9oEtqo0livLke9+csUkf2AOLzFsOvhkB/NocSQm33aySyNOphplx9yH2bgsHoEeR/aw/pMe4SkeDvNVfnemoB4PDNRUB9drFhzXOW5jypF9NQmBZaJDvJ+uK3mPXsWkEcxANn9mdRzYCEYCaVhgAZ5oQRnnT721mbFKpfc4kpI=

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Apply PHP regex replace on a multi-line repeted pattern

- by Hussain

Let's say I have this input: I can haz a listz0rs! # 42 # 126 I can haz another list plox? # Hello, world! # Welcome! I want to split it so that each set of hash-started lines becomes a list: I can haz a listz0rs! <ul> <li>42</li> <li>126</li> </ul> I can haz another list plox? <ul> <li>Hello, world!</li> <li>Welcome!</li> </ul> If I run the input against the regex "/(?:(?:(?<=^# )(.*)$)+)/m", I get the following result: Array ( [0] => Array ( [0] => 42 ) Array ( [0] => 126 ) Array ( [0] => Hello, world! ) Array ( [0] => Welcome! ) ) This is fine and dandy, but it doesn't distinguish between the two different lists. I need a way to either make the quantifier return a concatenated string of all the occurrences, or, ideally, an array of all the occurrences. Idealy, this should be my output: Array ( [0] = Array ( [0] = 42 [1] = 126 ) Array ( [0] = Hello, world! [1] = Welcome! ) ) Is there any way of achieving this, and if not, is there a close alternative? Thanks in advance!

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Any danger in calling flash messages html_safe?

- by PreciousBodilyFluids

I want a flash message that looks something like: "That confirmation link is invalid or expired. Click here to have a new one generated." Where "click here" is of course a link to another action in the app where a new confirmation link can be generated. Two drawbacks: One, since link_to isn't defined in the controller where the flash message is being set, I have to put the link html in myself. No big deal, but kind of messy. Number two: In order for the link to actually display properly on the page I have to html_safe the flash display function in the view, so now it looks like (using Haml): - flash.each do |name, message| = content_tag :div, message.html_safe This gives me pause. Everything else I html_safe has been HTML I've written myself in helpers and whatnot, but the contents of the flash hash are stored in a cookie client-side, and could conceivably be changed. I've thought through it, and I don't see how this could result in an XSS attack, but XSS isn't something I have a great understanding of anyway. So, two questions: 1. Is there any danger in always html_safe-ing all flash contents like this? 2. The fact that this solution is so messy (breaking MVC by using HTML in the controller, always html_safe-ing all flash contents) make me think I'm going about this wrong. Is there a more elegant, Rails-ish way to do this? I'm using Rails 3.0.0.beta3.

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Who likes #regions in Visual Studio?

- by Nicholas

Personally I can't stand region tags, but clearly they have wide spread appeal for organizing code, so I want to test the temperature of the water for other MS developer's take on this idea. My personal feeling is that any sort of silly trick to simplify code only acts to encourage terrible coding behavior, like lack of cohesion, unclear intention and poor or incomplete coding standards. One programmer told me that code regions helped encourage coding standards by making it clear where another programmer should put his or her contributions. But, to be blunt, this sounds like a load of horse manure to me. If you have a standard, it is the programmer's job to understand what that standard is... you should't need to define it in every single class file. And, nothing is more annoying than having all of your code collapsed when you open a file. I know that cntrl + M, L will open everything up, but then you have the hideous "hash region definition" open and closing lines to read. They're just irritating. My most stead fast coding philosophy is that all programmer should strive to create clear, concise and cohesive code. Region tags just serve to create noise and redundant intentions. Region tags would be moot in a well thought out and intentioned class. The only place they seem to make sense to me, is in automatically generated code, because you should never have to read that outside of personal curiosity.

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BCrypt says long, similar passwords are equivalent - problem with me, the gem, or the field of crypt

- by PreciousBodilyFluids

I've been experimenting with BCrypt, and found the following. If it matters, I'm running ruby 1.9.2dev (2010-04-30 trunk 27557) [i686-linux] require 'bcrypt' # bcrypt-ruby gem, version 2.1.2 @long_string_1 = 'f287ed6548e91475d06688b481ae8612fa060b2d402fdde8f79b7d0181d6a27d8feede46b833ecd9633b10824259ebac13b077efb7c24563fce0000670834215' @long_string_2 = 'f6ebeea9b99bcae4340670360674482773a12fd5ef5e94c7db0a42800813d2587063b70660294736fded10217d80ce7d3b27c568a1237e2ca1fecbf40be5eab8' def salted(string) @long_string_1 + string + @long_string_2 end encrypted_password = BCrypt::Password.create(salted('password'), :cost => 10) puts encrypted_password #=> $2a$10$kNMF/ku6VEAfLFEZKJ.ZC.zcMYUzvOQ6Dzi6ZX1UIVPUh5zr53yEu password = BCrypt::Password.new(encrypted_password) puts password.is_password?(salted('password')) #=> true puts password.is_password?(salted('passward')) #=> true puts password.is_password?(salted('75747373')) #=> true puts password.is_password?(salted('passwor')) #=> false At first I thought that once the passwords got to a certain length, the dissimilarities would just be lost in all the hashing, and only if they were very dissimilar (i.e. a different length) would they be recognized as different. That didn't seem very plausible to me, from what I know of hash functions, but I didn't see a better explanation. Then, I tried shortening each of the long_strings to see where BCrypt would start being able to tell them apart, and I found that if I shortened each of the long strings to 100 characters or so, the final attempt ('passwor') would start returning true as well. So now I don't know what to think. What's the explanation for this?

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The OpenID Provider issued an assertion for an Identifier whose discovery information did not match

- by Sohail

I used sample code from DotNetOpenAuth.net to become my own OpenID Provider (OpenIDProviderWebForm) everything worked fine and I was able to test my OP against NerdDinner. now I want to customize the identifier like --- http://www.mydomain.com/user.aspx/Hash(Username+PrivateKey)~Username. everything works on OP side but on the NerdDinner application when the app tries to do HttpRequestInfo clientResponseInfo = new HttpRequestInfo("GET", auth, auth.PathAndQuery, headers, null); response = RelyingParty.GetResponse(clientResponseInfo); (you find these two lines of codes in AuthController.cs from NerdDinner) the response contains below error: The OpenID Provider issued an assertion for an Identifier whose discovery information did not match. Assertion endpoint info: ClaimedIdentifier: http://localhost:57571/user.aspx/76208371132EC7F7A37472C8B4CC2CC37A05B707~sohail ProviderLocalIdentifier: http://localhost:57571/user.aspx/76208371132EC7F7A37472C8B4CC2CC37A05B707~sohail ProviderEndpoint: http://localhost:57571/server.aspx OpenID version: 2.0 Service Type URIs: Discovered endpoint info: [ { ClaimedIdentifier: http://localhost:57571/user.aspx/EA467E35736AC22EB60C04C2E9D9594263B60ECB~sohail ProviderLocalIdentifier: http://localhost:57571/user.aspx/EA467E35736AC22EB60C04C2E9D9594263B60ECB~sohail ProviderEndpoint: http://localhost:57571/server.aspx OpenID version: 2.0 Service Type URIs: http://specs.openid.net/auth/2.0/signon http://openid.net/extensions/sreg/1.1 }, { ClaimedIdentifier: http://localhost:57571/user.aspx/EA467E35736AC22EB60C04C2E9D9594263B60ECB~sohail ProviderLocalIdentifier: http://localhost:57571/user.aspx/EA467E35736AC22EB60C04C2E9D9594263B60ECB~sohail ProviderEndpoint: http://localhost:57571/server.aspx OpenID version: 1.0 Service Type URIs: http://openid.net/signon/1.0 http://openid.net/extensions/sreg/1.1 }, ] anybody can help me please?

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Type-safe mapping from Class<T> to Thing<T>

- by Joonas Pulakka

I want to make a map-kind of container that has the following interface: public <T> Thing<T> get(Class<T> clazz); public <T> void put(Class<T> clazz, Thing<T> thing); The interesting point is that the Ts in each Class<T><- Thing<T> pair is the same T, but the container should be able to hold many different types of pairs. Initially I tried a (Hash)Map. But, for instance, Map<Class<T>, Thing<T>> is not right, because then T would be same T for all pairs in that map. Of course, Map<Class<?>, Thing<?>> works, but then I don't have type-safety guarantees so that when I get(String.class), I can't be sure that I get a Thing<String> instance back. Is there a way to accomplish the kind of type safety that I'm looking for?

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MYSQL - SELECT ALL FROM TABLE if...

- by hornetbzz

Hello I have a (nice) mysql table built like this : Fields Datas id (pk) 1 2 3 4 5 6 master_id 1000 1000 1000 2000 2000 2000 ... master_name home home home shop shop shop ... type_data value common client value common client ... param_a foo_a 1 0 bar_a 0 1 ... param_b foo_b 1 0 bar_b 1 0 ... param_c foo_c 0 1 bar_c 0 1 ... ... ... ... ... ... ... ... ... All these datas are embed in a single table. Each datas are dispatched on 3 "columns" set (1 for the values, 1 for identifying if these are common values and one for identifying client values). It's not the best I got but many other scripts depends on this structure. I'd need sthg like this: SELECT parameters name (eg param_a, param_b..) and their values (eg foo_a, foo_b..) WHEN master_id=? AND type_data=(common or client) (eg for values=1 on the 2nd column) . in order to get the parameters hash like param_a => foo_a param_b => foo_b param_c => foo_c ... I could not succeed in self joining on the same table till now but I guess it should be feasible. (I'd like to avoid to do several queries) Thx in advance

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__toString magic and type coercion

- by TomcatExodus

I've created a Template class for managing views and their associated data. It implements Iterator and ArrayAccess, and permits "sub-templates" for easy usage like so: <p><?php echo $template['foo']; ?></p> <?php foreach($template->post as $post): ?> <p><?php echo $post['bar']; ?></p> <?php endforeach; ?> Anyways, rather than using inline core functions, such as hash() or date(), I figured it would be useful to create a class called TemplateData, which would act as a wrapper for any data stored in the templates. This way, I can add a list of common methods for formatting, for example: echo $template['foo']->asCase('upper'); echo $template['bar']->asDate('H:i:s'); //etc.. When a value is set via $template['foo'] = 'bar'; in the controllers, the value of 'bar' is stored in it's own TemplateData object. I've used the magic __toString() so when you echo a TemplateData object, it casts to (string) and dumps it's value. However, despite the mantra controllers and views should not modify data, whenever I do something like this: $template['foo'] = 1; echo $template['foo'] + 1; //exception It dies on a Object of class TemplateData could not be converted to int; Unless I recast $template['foo'] to a string: echo ((string) $template['foo']) + 1; //outputs 2 Sort of defeats the purpose having to jump through that hoop. Are there any workarounds for this sort of behavior that exist, or should I just take this as it is, an incidental prevention of data modification in views?

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GNU Make - Dependencies on non program code

- by Tim Post

A requirement for a program I am writing is that it must be able to trust a configuration file. To accomplish this, I am using several kinds of hashing algorithms to generate a hash of the file at compile time, this produces a header with the hashes as constants. Dependencies for this are pretty straight forward, my program depends on config_hash.h, which has a target that produces it. The makefile looks something like this : config_hash.h: $(SH) genhash config/config_file.cfg > $(srcdir)/config_hash.h $(PROGRAM): config_hash.h $(PROGRAM_DEPS) $(CC) ... ... ... I'm using the -M option to gcc, which is great for dealing with dependencies. If my header changes, my program is rebuilt. My problem is, I need to be able to tell if the config file has changed, so that config_hash.h is re-generated. I'm not quite sure how explain that kind of dependency to GNU make. I've tried listing config/config_file.cfg as a dependency for config_hash.h, and providing a .PHONY target for config_file.cfg without success. Obviously, I can't rely on the -M switch to gcc to help me here, since the config file is not a part of any object code. Any suggestions? Unfortunately, I can't post much of the Makefile, or I would have just posted the whole thing.

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template files in python

- by saminny

I am trying to use python for translating a set of templates to a set of configuration files based on values taken from a main configuration file. However, I am having certain issues. Consider the following example of a template file. file1.cfg.template %(CLIENT1)s %(HOST1)s %(PORT1)d C %(COMPID1)s %(CLIENT2)s %(HOST2)s %(PORT2)d C %(COMPID2)s This file contains an entry for each client. There are hundreds of config files like this and I don't want to have logic for each type of config file. Python should do the replacements and generate config files automatically given a set of global values read from a main xml config file. However, in the above example, if CLIENT2 does not exist, how do I delete that line? I expect Python would generate the config file using the following simple code: os.open("file1.cfg.template").read() & myhash where myhash is hash of all configuration parameters which may not contain CLIENT2 at all. In the case it does not contain CLIENT2, I want that line to disappear from the file. Is it possible to insert some 'IF' block in the file and have python evaluate it? Thanks for your help. Any suggestions most welcome.

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Hashtable resizing leaks memory

- by thpetrus

I wrote a hashtable and it basically consists of these two structures: typedef struct dictEntry { void *key; void *value; struct dictEntry *next; } dictEntry; typedef struct dict { dictEntry **table; unsigned long size; unsigned long items; } dict; dict.table is a multidimensional array, which contains all the stored key/value pair, which again are a linked list. If half of the hashtable is full, I expand it by doubling the size and rehashing it: dict *_dictRehash(dict *d) { int i; dict *_d; dictEntry *dit; _d = dictCreate(d->size * 2); for (i = 0; i < d->size; i++) { for (dit = d->table[i]; dit != NULL; dit = dit->next) { _dictAddRaw(_d, dit); } } /* FIXME memory leak because the old dict can never be freed */ free(d); // seg fault return _d; } The function above uses the pointers from the old hash table and stores it in the newly created one. When freeing the old dict d a Segmentation Fault occurs. How am I able to free the old hashtable struct without having to allocate the memory for the key/value pairs again?

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TicTacToe strategic reduction

- by NickLarsen

I decided to write a small program that solves TicTacToe in order to try out the effect of some pruning techniques on a trivial game. The full game tree using minimax to solve it only ends up with 549,946 possible games. With alpha-beta pruning, the number of states required to evaluate was reduced to 18,297. Then I applied a transposition table that brings the number down to 2,592. Now I want to see how low that number can go. The next enhancement I want to apply is a strategic reduction. The basic idea is to combine states that have equivalent strategic value. For instance, on the first move, if X plays first, there is nothing strategically different (assuming your opponent plays optimally) about choosing one corner instead of another. In the same situation, the same is true of the center of the walls of the board, and the center is also significant. By reducing to significant states only, you end up with only 3 states for evaluation on the first move instead of 9. This technique should be very useful since it prunes states near the top of the game tree. This idea came from the GameShrink method created by a group at CMU, only I am trying to avoid writing the general form, and just doing what is needed to apply the technique to TicTacToe. In order to achieve this, I modified my hash function (for the transposition table) to enumerate all strategically equivalent positions (using rotation and flipping functions), and to only return the lowest of the values for each board. Unfortunately now my program thinks X can force a win in 5 moves from an empty board when going first. After a long debugging session, it became apparent to me the program was always returning the move for the lowest strategically significant move (I store the last move in the transposition table as part of my state). Is there a better way I can go about adding this feature, or a simple method for determining the correct move applicable to the current situation with what I have already done?

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Should I Use Anchor, Button Or Form Submit For "Follow" Feature In Rails

- by James

I am developing an application in Rails 3 using a nosql database. I am trying to add a "Follow" feature similar to twitter or github. In terms of markup, I have determined that there are three ways to do this. 1) Use a regular anchor. (Github Uses This Method) <a href="/users/follow?target=Joe">Follow</a> 2) Use a button. (Twitter Uses This Method) <button href="/friendships/create/">Follow</button> 3) Use a form with a submit button. (Has some advantages for me, but I haven't see anyone do it yet.) <form method="post" id="connection_new" class="connection_new" action="/users/follow"> <input type="hidden" value="60d7b563355243796dd8496e17d36329" name="target" id="target"> <input type="submit" value="Follow" name="commit" id="connection_submit"> </form> Since I want to store the user_id in the database and not the username, options 1 and 2 will force me to do a database query to get the actual user_id, whereas option 3 will allow me to store the user_id in a hidden form field so that I don't have to do any database lookups. I can just get the id from the params hash on form submission. I have successfully got each of these methods working, but I would like to know what is the best way to do this. Which way is more semantic, secure, better for spiders, etc...? Is there a reason both twitter and github don't use forms to do this? Any guidance would be appreciated. I am leaning towards using the form method since then I don't have to query the db to get the id of the user, but I am worried that there must be a reason the big guys are just using anchors or buttons for this. I am a newb so go easy on me if I am totally missing something. Thanks!

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Apply PHP regex replace on a multi-line repeated pattern

- by Hussain

Let's say I have this input: I can haz a listz0rs! # 42 # 126 I can haz another list plox? # Hello, world! # Welcome! I want to split it so that each set of hash-started lines becomes a list: I can haz a listz0rs! <ul> <li>42</li> <li>126</li> </ul> I can haz another list plox? <ul> <li>Hello, world!</li> <li>Welcome!</li> </ul> If I run the input against the regex "/(?:(?:(?<=^# )(.*)$)+)/m", I get the following result: Array ( [0] => Array ( [0] => 42 ) [1] => Array ( [0] => 126 ) [2] => Array ( [0] => Hello, world! ) [3] => Array ( [0] => Welcome! ) ) This is fine and dandy, but it doesn't distinguish between the two different lists. I need a way to either make the quantifier return a concatenated string of all the occurrences, or, ideally, an array of all the occurrences. Ideally, this should be my output: Array ( [0] => Array ( [0] => 42 [1] => 126 ) [1] => Array ( [0] => Hello, world! [1] => Welcome! ) ) Is there any way of achieving this, and if not, is there a close alternative? Thanks in advance!

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Ruby TypeErrors involving `expected Data`

- by Kenny Peng

I've ran into situations where I have gotten these expected Data errors before, but they have always pointed to ActiveRecord not playing well with other libraries in the past. This piece of code: def load(kv_block, debug=false) # Converts a string block to a Hash using split kv_map = StringUtils.kv_array_to_hash(kv_block) # Loop through each key, value kv_map.each do |mem,val| # Format the member from camel case to underscore member = mem.camel_to_underscore() # If the object includes a method to set the key (i.e. the key # is a member of self), invoke the method, setting the value of # the member) if self.methods.include?(member.to_set_method_name()) then # Exception thrown here self.send(member.to_set_method_name(), val) # Else, check for the same case, this time for an instance variable elsif self.instance_variable_defined?(member.to_instance_var_name()) self.instance_variable_set(member.to_instance_var_name(), val) # Else, complain that the object doesn't understand the key with # respect to its class definition. else raise ArgumentError, "I don't know what to do with #{member}. #{self.class} does not have a member or function called #{member}" end end end produces the error wrong argument type #<Class:0x11a02088> (expected Data) (TypeError) in the each loop on the first if test. I've inspected a post-mortem debugging instance using rdebug, and running that line manually, it works without a hitch. Has anyone seen this error before and what's been your solution to it? I used to think it was ActiveRecord and other gems stomping on each other's definitions, but I removed any references to ActiveRecord and this still occurs.

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how i can retrive files from folder on hard-disk and how to display uplaoded file data into a textar

- by Deepak Narwal

I have made a application form in which i am asking for username,password,email id and user's resume.Now after uploading resume i am storing it into hard disk into htdocs/uploadedfiles/..in a format something like this username_filename.In database i am storing file name,file size,file type.Some coading for this i am showing here $filesize=$_FILES['file']['size']; $filename=$_FILES['file']['name']; $filetype=$_FILES['file']['type']; $temp_name=$_FILES['file']['tmp_name']; //temporary name of uploaded file $pwd_hash = hash('sha1',$_POST['password']); $target_path = "uploadedfiles/"; $target_path = $target_path.$_POST['username']."_".basename( $_FILES['file']['name']); move_uploaded_file($_FILES['file']['tmp_name'], $target_path) ; $sql="insert into employee values ('NULL','{$_POST[username]}','{$pwd_hash}','{$filename}','{$filetype}','$filesize',NOW())"; Now i have two questions 1.NOw how i can display this file data into a textarea(something like naukri.com resume section) 2.How one can retrive that resume file from folder on hard-disk.What query should i write to fetch this file from that folder.I know how to retrive data from database but i dont know how to retrive data from a folder in hard-disk like in the case if user want to delete this file or he wnat to download this file.How i can do this

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setting cookies

- by aharon

Okay, so I'm trying to set cookies using Ruby. I'm in a Rack environment. response[name]=value will add an HTTP header into the HTTP headers hash rack has. I know that it works. The following method doesn't work: def set_cookie(opts={}) args = { :name => nil, :value => nil, :expires => Time.now+314, :path => '/', :domain => Cambium.uri #contains the IP address of the dev server this is running on }.merge(opts) raise ArgumentError, ":name and :value are mandatory" if args[:name].nil? or args[:value].nil? response['Set-Cookie']="#{args[:name]}=#{args[:value]}; expires=#{args[:expires].clone.gmtime.strftime("%a, %d-%b-%Y %H:%M:%S GMT")}; path=#{args[:path]}; domain=#{args[:domain]}" end Why not? And how can I solve it? Thanks.

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how to store a file handle in perl class

- by Haiyuan Zhang

please look at the following code first. #! /usr/bin/perl package foo; sub new { my $pkg = shift; my $self = {}; my $self->{_fd} = undef; bless $self, $pkg; return $self; } sub Setfd { my $self = shift; my $fd = shift; $self_->{_fd} = $fd; } sub write { my $self = shift; print $self->{_fd} "hello word"; } my $foo = new foo; My intention is to store a file handle within a class using hash. the file handle is undefined at first, but can be initilized afterwards by calling Setfd function. then write can be called to actually write string "hello word" to a file indicated by the file handle, supposed that the file handle is the result of a success "write" open. but, perl compiler just complains that there are syntax error in the "print" line. can anyone of you tells me what's wrong here? thanks in advance.

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Database abstraction/adapters for ruby

- by Stiivi

What are the database abstractions/adapters you are using in Ruby? I am mainly interested in data oriented features, not in those with object mapping (like active record or data mapper). I am currently using Sequel. Are there any other options? I am mostly interested in: simple, clean and non-ambiguous API data selection (obviously), filtering and aggregation raw value selection without field mapping: SELECT col1, col2, col3 = [val1, val2, val3] not hash of { :col1 = val1 ...} API takes into account table schemas 'some_schema.some_table' in a consistent (and working) way; also reflection for this (get schema from table) database reflection: get list of table columns, their database storage types and perhaps adaptor's abstracted types table creation, deletion be able to work with other tables (insert, update) in a loop enumerating selection from another table without requiring to fetch all records from table being enumerated Purpose is to manipulate data with unknown structure at the time of writing code, which is the opposite to object mapping where structure or most of the structure is usually well known. I do not need the object mapping overhead. What are the options, including back-ends for object-mapping libraries?

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Generics vs inheritance (when no collection classes are involved)

- by Ram

This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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Haskell lazy I/O and closing files

- by Jesse

I've written a small Haskell program to print the MD5 checksums of all files in the current directory (searched recursively). Basically a Haskell version of md5deep. All is fine and dandy except if the current directory has a very large number of files, in which case I get an error like: <program>: <currentFile>: openBinaryFile: resource exhausted (Too many open files) It seems Haskell's laziness is causing it not to close files, even after its corresponding line of output has been completed. The relevant code is below. The function of interest is getList. import qualified Data.ByteString.Lazy as BS main :: IO () main = putStr . unlines =<< getList "." getList :: FilePath -> IO [String] getList p = let getFileLine path = liftM (\c -> (hex $ hash $ BS.unpack c) ++ " " ++ path) (BS.readFile path) in mapM getFileLine =<< getRecursiveContents p hex :: [Word8] -> String hex = concatMap (\x -> printf "%0.2x" (toInteger x)) getRecursiveContents :: FilePath -> IO [FilePath] -- ^ Just gets the paths to all the files in the given directory. Are there any ideas on how I could solve this problem? The entire program is available here: http://haskell.pastebin.com/PAZm0Dcb

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Using ant, rename a directory without knowing the full path?

- by mixonic

Howdy friends, Given a zipfile with an unknown directory, how can I rename or move that directory to a normalized path?  <target name="get.remote">  <get src="http://myhost.com/package.zip" dest="package.zip"/>  <unzip src="package.zip" dest="./"/>   <delete file="package.zip"/>   <mkdir dir="package" />  <move todir="package/"> <fileset dir="."> <include name="package-*/*"/> </fileset> </move> </target> I'm not much of an ant user, any insight would be helpful. Thanks much, -Matt

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What is the difference between a restful route method for getting an index vs. creating a new object

- by Jason

According to rake routes, there's the same path for getting an index of objects as there is for creating a new object: cars GET /cars(.:format) {:controller=>"plugs", :what=>"car", :action=>"index"} POST /cars(.:format) {:controller=>"plugs", :what=>"car", :action=>"create"} Obviously, the HTTP verb is what distinguishes between them. I want the "create" version of the cars_path method, not the "index" version. My question is what route method do you invoke to choose the one you want? I'm telling cucumber what path to generate with this: when /the car plug preview page for "(.+)"/ cars_path(:action => :create, :method => :post) ...but it always chooses the "index" action, not "create". I've tried lots of combinations for the hash argument following cars_path and nothing changes it from choosing "index" instead of "create". I'll get an error like this: cars_url failed to generate from {:controller=>"plugs", :method=>:post, :what=>"car", :action=>"create"}, expected: {:controller=>"plugs", :what=>"car", :action=>"index"}, diff: {:method=>:post, :action=>"index"} (ActionController::RoutingError) This seems like a very simple question but I've had no luck googling for it, so could use some advice. Thanks.

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