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• Java: How to workaround the lack of Equatable interface?

  - by java.is.for.desktop

  Hello, everyone! As far as I know, things such as SortedMap or SortedSet, use compareTo (rather than equals) on Comparable<?> types for checking equality (contains, containsKey). But what if certain types are equatable by concept, but not comparable? I have to declare a Comparator<?> and override the method int compareTo(T o1, To2). OK, I can return 0 for instances which are considered equal. But, for unqeual instances, what do I return when an order is not evident? Is the approach of using SortedMap or SortedSet on equatable but (by concept) not comparable types good anyway? Thank you! EDIT: I don't want to store things sorted, but would I use "usual" Map and Set, I couldn't "override" the equality-behavior. EDIT 2: Why I can't just override equals(...): I need to alter the equality-behavior of a foreign class. Can't edit it. EDIT 3: Just think of .NET: They have IEquatable interface which cat alter the equality-behavior without touching the comparable behavior.

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• StrcutureMap Wiring - Sanity Check Please

  - by Steve Ward

  Hi - Im new to IOC and StructureMap and have an n-level application and am looking at how to setup the wirings (ForRequestedType ...) and just want to check with people with more experience that this is the best way of doing it! I dont want my UI application object to reference my persistence layer directly so am not able to wire everything up in this UI project. I now have it working by defining a Registry class in each project which wires up the types in the project as needed. The layer above registers its types and also calls the assembly below and looks for registries so that all types are registered throught the hierrachy. E.g. I have UI, Service, Domain, and Persistence libraries. In my service layer the registry looks like Scan(x => { x.Assembly("MyPersistenceProject"); x.LookForRegistries(); }); ForRequestedType<IService>().TheDefault.Is.OfConcreteType<MyService>(); Is this a recommended way of doing this in a setup such as this? Are there better ways and what are the advantages / disadvantages of these approaches in this case?

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• [Database] How to model this one-to-one relation?

  - by pbean

  I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them. For example: a "general user", which has an e-mail address and "admin user", which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in. In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work. How should I model this effectively? I can't just create two tables, because then I can't force a unique constaint on the user name. I also can't put them all in just one table, because they have different types of specific information associated to them. I think I might need 3 seperate tables, one for "users" (with user name and password), one for the "general users" and another one for the "admin users", but how would the relations between these work? Or is there another solution? (By the way, the target DBMS is MySQL, so I don't think generalization is supported in the database system itself).

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• A feeling that I'm not that good developer

  - by Karim

  Hi, Im having a strange feeling, but let me first introduce myself as a software developer. I started to program when I was still a kid, I had about 10 or 11 years. I really enjoy my work and never get bored from it. It's amazing how somebody could be paid for what he really likes to do and would be doing it anyway even for free. WHen I first started to program, I was feeling proud of what I was doing, each application I built was for me a success and after 2-3 year I had a feeling that I'm a coding guru. It was a nice feeling ;-) But the more I was in the field, the more types of software I started to develop I was starting to have a feeling that I'm completely wrong in that I'm guru. I felt that I'm not even a mediocre developer. Each new field I start to work on is giving me this feeling. Like when I once developed a device driver for a client, I saw how much I need to learn about device drivers. When I developed a video filter for an application, I saw how much do I still need to learn about DirectShow, Color Spaces, and all the theory behind that. The worst thing was when I started to learn algorithms. It was several years ago. I knew then the basic structures and algorithms like the sorting, some types of trees, some hashtables, strings etc.. and when I really wanted to learn a group of structures I learned about 5-6 new types and saw that in fact even this small group has several hundred subtypes of structures. It's depressing how little time people have in their lives to learn all this stuff. I'm now a software developer with about 10 years of experience and I still feel that I'm not a proficient developer when I think about things that others do in the industry. Is this normal what I'm experiencing or is it a sign of a destructive excessive ambition? Thanks in advance for any comments.

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• dll's loaded through reflection

  - by Seattle Leonard

  Ok, I got a strange one here and I want to know if any of you have ever run accross anything like it. So I've got this web app that loads up a bunch of dll's through reflection. Basically it looks for Types that are derived from certain abstract types and adds them to the list of things it can make. Here's the weird part. While developing there is never a problem. When installing it, there is never a problem to start with. Then, at a seemingly random time, the application breaks while trying to find all the types. I've had 2 sites sitting side by side and one worked while the other did not, and they were configured exactly(and I mean exactly) the same. IISRESET's never helped, but this did: I simply moved all the dll's out of the bin directory then moved them back. That's right I just moved them out of the bin directory then put them right back where they came from and everything worked fine. Any ideas?

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• Extract data from PostgreSQL DB without using pg_dump

  - by John Horton

  There is a PostgreSQL database on which I only have limited access (e.g, I can't use pg_dump). I am trying to create a local "mirror" by exporting certain tables from the database. I do not have the permissions needed to just dump a table as SQL from within psql. Right now, I just have a Python script that iterates through my table_names, selects all fields and then exports them as a CSV: for table_name, file_name in zip(table_names, file_names): cmd = """echo "\\\copy (select * from %s)" to stdout WITH CSV HEADER | psql -d remote_db | gzip > ./%s/%s.gz"""%(table_name,dir_name,file_name) os.system(cmd) I would like to not use CSV if possible, as I lose the field types and the encoding can get messed up. First best would probably be some way of getting the generating SQL code for the table using \copy. Next best would be XML, ideally with some way of preserving the field types. If that doesn't work, I think the final option might be two queries---one to get the field data types, the other to get the actual data. Any thoughts or advice would be greatly appreciated - thanks!

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• How do I dispatch to a method based on a parameter's runtime type in C# < 4?

  - by Evan Barkley

  I have an object o which guaranteed at runtime to be one of three types A, B, or C, all of which implement a common interface I. I can control I, but not A, B, or C. (Thus I could use an empty marker interface, or somehow take advantage of the similarities in the types by using the interface, but I can't add new methods or change existing ones in the types.) I also have a series of methods MethodA, MethodB, and MethodC. The runtime type of o is looked up and is then used as a parameter to these methods. public void MethodA(A a) { ... } public void MethodB(B b) { ... } public void MethodC(C c) { ... } Using this strategy, right now a check has to be performed on the type of o to determine which method should be invoked. Instead, I would like to simply have three overloaded methods: public void Method(A a) { ... } // these are all overloads of each other public void Method(B b) { ... } public void Method(C c) { ... } Now I'm letting C# do the dispatch instead of doing it manually myself. Can this be done? The naive straightforward approach doesn't work, of course: Cannot resolve method 'Method(object)'. Candidates are: void Method(A) void Method(B) void Method(C)

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• Using LINQ to map dynamically (or construct projections)

  - by CodeGrue

  I know I can map two object types with LINQ using a projection as so: var destModel = from m in sourceModel select new DestModelType {A = m.A, C = m.C, E = m.E} where class SourceModelType { string A {get; set;} string B {get; set;} string C {get; set;} string D {get; set;} string E {get; set;} } class DestModelType { string A {get; set;} string C {get; set;} string E {get; set;} } But what if I want to make something like a generic to do this, where I don't know specifically the two types I am dealing with. So it would walk the "Dest" type and match with the matching "Source" types.. is this possible? Also, to achieve deferred execution, I would want it just to return an IQueryable. For example: public IQueryable<TDest> ProjectionMap<TSource, TDest>(IQueryable<TSource> sourceModel) { // dynamically build the LINQ projection based on the properties in TDest // return the IQueryable containing the constructed projection } I know this is challenging, but I hope not impossible, because it will save me a bunch of explicit mapping work between models and viewmodels.

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• MVC2 Modelbinder for List of derived objects

  - by user250773

  I want a list of different (derived) object types working with the Default Modelbinder in Asp.net MVC 2. I have the following ViewModel: public class ItemFormModel { [Required(ErrorMessage = "Required Field")] public string Name { get; set; } public string Description { get; set; } [ScaffoldColumn(true)] //public List<Core.Object> Objects { get; set; } public ArrayList Objects { get; set; } } And the list contains objects of diffent derived types, e.g. public class TextObject : Core.Object { public string Text { get; set; } } public class BoolObject : Core.Object { public bool Value { get; set; } } It doesn't matter if I use the List or the ArrayList implementation, everything get's nicely scaffolded in the form, but the modelbinder doesn't resolve the derived object type properties for me when posting back to the ActionResult. What could be a good solution for the Viewmodel structure to get a list of different object types handled? Having an extra list for every object type (e.g. List, List etc.) seems to be not a good solution for me, since this is a lot of overhead both in building the viewmodel and mapping it back to the domain model. Thinking about the other approach of binding all properties in a custom model binder, how can I make use the data annotations approach here (validating required attributes etc.) without a lot of overhead?

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• Would making plain int 64-bit break a lot of reasonable code?

  - by R..

  Until recently, I'd considered the decision by most systems implementors/vendors to keep plain int 32-bit even on 64-bit machines a sort of expedient wart. With modern C99 fixed-size types (int32_t and uint32_t, etc.) the need for there to be a standard integer type of each size 8, 16, 32, and 64 mostly disappears, and it seems like int could just as well be made 64-bit. However, the biggest real consequence of the size of plain int in C comes from the fact that C essentially does not have arithmetic on smaller-than-int types. In particular, if int is larger than 32-bit, the result of any arithmetic on uint32_t values has type signed int, which is rather unsettling. Is this a good reason to keep int permanently fixed at 32-bit on real-world implementations? I'm leaning towards saying yes. It seems to me like there could be a huge class of uses of uint32_t which break when int is larger than 32 bits. Even applying the unary minus or bitwise complement operator becomes dangerous unless you cast back to uint32_t. Of course the same issues apply to uint16_t and uint8_t on current implementations, but everyone seems to be aware of and used to treating them as "smaller-than-int" types.

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• C# Generics Question

  - by TheCloudlessSky

  Would it be possible to do something like the following in c#? Basically TParent and TChildren should be types of the class A but not necessairly have the same types that were passed in. I know this may sound confusing but I want to strongly type the children and parents of a particular object, but at the same time they must be of the same type. Because TParent inherits from A this would imply that it requires type parameters that inherit from A but using potentially different types. public class A<TParent, TChildren> where TParent : A where TControls : A { TParent Parent; List<TChildren> Children; } or more easily seen here: public class A<TParent, TChildren> where TParent : A<?, ?> where TChildren : A<?, ?> { TParent Parent; List<TChildren> Children; } I hope this isn't too confusing. Is this at all possible? Thanks :)

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• Type classe, generic memoization

  - by nicolas

  Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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• How to encapsulate a third party complex object structure?

  - by tangens

  Motivation Currently I'm using the java parser japa to create an abstract syntax tree (AST) of a java file. With this AST I'm doing some code generation (e.g.: if there's an annotation on a method, create some other source files, ...) Problem When my code generation becomes more complex, I've to dive deeper into the structure of the AST (e.g. I have to use visitors to extract some type information of method parameters). But I'm not sure if I want to stay with japa or if I will change the parser library later. Because my code generator uses freemarker (which isn't good at automatic refactoring) I want the interface that it uses to access the AST information to be stable, even if I decide to change the java parser. Question What's the best way to encapsulate complex datastructures of third party libraries? I could create my own datatypes and copy the parts of the AST that I need into these. I could create lots of specialized access methods that work with the AST and create exactly the infos I need (e.g. the fully qualified return type of a method as one string, or the first template parameter of a class). I could create wrapper classes for the japa datastructures I currently need and embed the japa types inside, so that I can delegate requests to the japa types and transform the resulting japa types to my wrapper classes again. Which solution should I take? Are there other (better) solutions to this problem?

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• Syntax for documenting JSON structure

  - by Roman A. Taycher

  So I'm trying to document the format of the json returned by an api I am writing against and I'd like to know if there is any popular format for the documentation of json structure. Note I'm not trying to to test or validate anything, I'm just using this for documentation. Also some ways to add comments to non-constants(items always returned w/ the same value) would be nice. This the not totally thought out scheme I'm currently using: Plain names refer to identifiers or types. Some types have type-comment Strings that appear to be constant(always returned for that type of request) strings are "str" Constant Numbers would be just the number Constant null is null Booleans are true/false for constant booleans or Boolean otherwise [a,b,c] are lists with 3 items a,b,c [... ...] is a list of repeating elements of some types/constants/patterns {a:A,b:B,c:c} and {... ...} is the same for a dictionary. example: story := [header,footer] header := {"data":realHeader,"kind":"Listing"} realHeader := {"after": null, "before": null, "children": [{"data": realRealHeader, "kind": "t3"}], "modhash": ""} footer := {"data":AlmostComments,"kind":"Listing"} AlmostComments := {"data": {"after": null, "before": null, "children": comments, "modhash": ""}, "kind": "t1"} comments := [...{"data":comment, "kind":"t1"}...] realRealHeader := {"author": string, "clicked": boolean, "created": int, "created_utc": int, "domain": "code.reddit.com", "downs": int, "hidden": boolean, "id": string-id, "is_self": boolean, "levenshtein": null, "likes": null, "media": null, "media_embed": { }, "name": string-id, "num_comments": int, "over_18": false, "permalink": string-urlLinkToStoryStartingFrom/r, "saved": false, "score": int, "selftext": string, "selftext_html": string-html, "subreddit": string-subredditname, "subreddit_id": string-id, "thumbnail": "", "title": string, "ups": int, "url": "http://code.reddit.com/" } comments := { "author": string, "body": string-body_html-wout-html, "body_html": string-html-formated, "created": int, "created_utc": int, "downs": int, "id": string-id, "levenshtein": null, "likes": null, "link_id": string-id, "name": string-id", "parent_id": string-id, "replies": AlmostComments or null, "subreddit": string-subredditname, "subreddit_id": string-id, "ups": int }

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• Callback function and function pointer trouble in C++ for a BST

  - by Brendon C.

  I have to create a binary search tree which is templated and can deal with any data types, including abstract data types like objects. Since it is unknown what types of data an object might have and which data is going to be compared, the client side must create a comparison function and also a print function (because also not sure which data has to be printed). I have edited some C code which I was directed to and tried to template, but I cannot figure out how to configure the client display function. I suspect variable 'tree_node' of class BinarySearchTree has to be passed in, but I am not sure how to do this. For this program I'm creating an integer binary search tree and reading data from a file. Any help on the code or the problem would be greatly appreciated :) Main.cpp #include "BinarySearchTreeTemplated.h" #include <iostream> #include <fstream> #include <string> using namespace std; /*Comparison function*/ int cmp_fn(void *data1, void *data2) { if (*((int*)data1) > *((int*)data2)) return 1; else if (*((int*)data1) < *((int*)data2)) return -1; else return 0; } static void displayNode() //<--------NEED HELP HERE { if (node) cout << " " << *((int)node->data) } int main() { ifstream infile("rinput.txt"); BinarySearchTree<int> tree; while (true) { int tmp1; infile >> tmp1; if (infile.eof()) break; tree.insertRoot(tmp1); } return 0; } BinarySearchTree.h (a bit too big to format here) http://pastebin.com/4kSVrPhm

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• What are the default return values for operator< and operator[] in C++ (Visual Studio 6)?

  - by DustOff

  I've inherited a large Visual Studio 6 C++ project that needs to be translated for VS2005. Some of the classes defined operator< and operator[], but don't specify return types in the declarations. VS6 allows this, but not VS2005. I am aware that the C standard specifies that the default return type for normal functions is int, and I assumed VS6 might have been following that, but would this apply to C++ operators as well? Or could VS6 figure out the return type on its own? For example, the code defines a custom string class like this: class String { char arr[16]; public: operator<(const String& other) { return something1 < something2; } operator[](int index) { return arr[index]; } }; Would VS6 have simply put the return types for both as int, or would it have been smart enough to figure out that operator[] should return a char and operator< should return a bool (and not convert both results to int all the time)? Of course I have to add return types to make this code VS2005 C++ compliant, but I want to make sure to specify the same type as before, as to not immediately change program behavior (we're going for compatibility at the moment; we'll standardize things later).

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• Porting Symbian C++ to Android NDK

  - by Donal Rafferty

  I've been given some Symbian C++ code to port over for use with the Android NDK. The code has lots of Symbian specific code in it and I have very little experience of C++ so its not going very well. The main thing that is slowing me down is trying to figure out the alternatives to use in normal C++ for the Symbian specific code. At the minute the compiler is throwing out all sorts of errors for unrecognised types. From my recent research these are the types that I believe are Symbian specific: TInt, TBool, TDesc8, RSocket, TInetAddress, TBuf, HBufc, RPointerArray Changing TInt and TBool to int and bool respectively works in the compiler but I am unsure what to use for the other types? Can anyone help me out with them? Especially TDesc, TBuf, HBuf. Also Symbian has a two phase contructor using NewL and NewLc But would changing this to a normal C++ constructor be ok? Finally Symbian uses the clean up stack to help eliminate memory leaks I believe, would removing the clean up stack code be acceptable, I presume it should be replaced with try/catch statements?

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• How to alter Postgres table data based on its contents?

  - by williamjones

  This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google. I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row. There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these). It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database. First, a quick threshold question of, is this a good idea? Any feedback or anything I missed? Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?

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• An array problem in C++

  - by manugupt1

  To access the array indice at the xth position we can use some sort of illustration as shown below #include<iostream> using namespace std; int main(){ float i[20]; for(int j=0;j<=20;j++) i[j]=0; } However the following piece of code does not work #include<iostream> using namespace std; float oldrand[55]; int jrand; void advance_random(){ int j1; float new_random; for(j1=0;j1<=23;j1++){ int temp = j1+30; new_random = (oldrand[j1]) - (oldrand[temp]); if(new_random <0.0) new_random = new_random+1; oldrand[j1] = new_random; } for(j1=24;j1<=54;j1++){ new_random[j1] = oldrand[j1] - oldrand[j1-23]; if(new_random[j1]<0.0) new_random[j1] = new_random + 1; oldrand[j1]=new_random; } } I recieve the following error ga.cpp:20: error: invalid types ‘float[int]’ for array subscript ga.cpp:21: error: invalid types ‘float[int]’ for array subscript ga.cpp:22: error: invalid types ‘float[int]’ for array subscript I am not able to find a mistake in my code please help me

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• importing symbols from python package into caller's namespace

  - by Paul C

  I have a little internal DSL written in a single Python file that has grown to a point where I would like to split the contents across a number of different directories + files. The new directory structure currently looks like this: dsl/ __init__.py types/ __init__.py type1.py type2.py and each type file contains a class (e.g. Type1). My problem is that I would like to keep the implementation of code that uses this DSL as simple as possible, something like: import dsl x = Type1() ... This means that all of the important symbols should be available directly in the user's namespace. I have tried updating the top-level __init__.py file to import the relevant symbols: from types.type1 import Type1 from types.type2 import Type2 ... print globals() the output shows that the symbols are imported correctly, but they still aren't present in the caller's code (the code that's doing the import dsl). I think that the problem is that the symbols are actually being imported to the 'dsl' namespace. How can I change this so that the classes are also directly available in the caller's namespace?

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• Faster Insertion of Records into a Table with SQLAlchemy

  - by Kyle Brandt

  I am parsing a log and inserting it into either MySQL or SQLite using SQLAlchemy and Python. Right now I open a connection to the DB, and as I loop over each line, I insert it after it is parsed (This is just one big table right now, not very experienced with SQL). I then close the connection when the loop is done. The summarized code is: log_table = schema.Table('log_table', metadata, schema.Column('id', types.Integer, primary_key=True), schema.Column('time', types.DateTime), schema.Column('ip', types.String(length=15)) .... engine = create_engine(...) metadata.bind = engine connection = engine.connect() .... for line in file_to_parse: m = line_regex.match(line) if m: fields = m.groupdict() pythonified = pythoninfy_log(fields) #Turn them into ints, datatimes, etc if use_sql: ins = log_table.insert(values=pythonified) connection.execute(ins) parsed += 1 My two questions are: Is there a way to speed up the inserts within this basic framework? Maybe have a Queue of inserts and some insertion threads, some sort of bulk inserts, etc? When I used MySQL, for about ~1.2 million records the insert time was 15 minutes. With SQLite, the insert time was a little over an hour. Does that time difference between the db engines seem about right, or does it mean I am doing something very wrong?

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• I have a bunch of template parameters that I want to hide from my users. How can I do this?

  - by Alex

  I have a superclass which is defined in terms of a few internal types it uses. Subclassing is performed as so: template <class InternalType1, class InternalType2> class Super { ... } class Sub : Super <interalTypeClass1, interalTypeClass2> { ... } But when I want to write a function that takes a pointer to the superclass, this happens : template <class InternalType1, class InternalType2> void function(Super<InternalType1, InternalType2>* in) { ... } The user really shouldn't know anything about the inside classes, and should really just concern himself with the use of the function. Some of these template lists become very very large, and expecting the user to pass them every time is wasteful, in my opinion. Any suggestions? EDIT: The function needs to know the internal types in use, so unless there is a way to access template types at compile time, I think there is no solution? Potential solution: Have each class do the following: #define SubTemplateArgs <SubTypeName, SubInternalType1, SubInternalType2> ?

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• When to use reinterpret_cast?

  - by HeretoLearn

  I am little confused with the applicability of reinterpret_cast vs static_cast. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static. This is the cast the C++ compiler uses internally for implicit casts also. reinterpret_cast are applicable in two scenarios, convert integer types to pointer types and vice versa or to convert one pointer type to another. The general idea I get is this is unportable and should be avoided. Where I am a little confused is one usage which I need, I am calling C++ from C and the C code needs to hold on to the C++ object so basically it holds a void*. What cast should be used to convert between the void * and the Class type? I have seen usage of both static_cast and reinterpret_cast? Though from what I have been reading it appears static is better as the cast can happen at compile time? Though it says to use reinterpret_cast to convert from one pointer type to another?

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• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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• Make conversion to a native type explicit in C++

  - by Tal Pressman

  I'm trying to write a class that implements 64-bit ints for a compiler that doesn't support long long, to be used in existing code. Basically, I should be able to have a typedef somewhere that selects whether I want to use long long or my class, and everything else should compile and work. So, I obviously need conversion constructors from int, long, etc., and the respective conversion operators (casts) to those types. This seems to cause errors with arithmetic operators. With native types, the compiler "knows" that when operator*(int, char) is called, it should promote the char to int and call operator*(int, int) (rather than casting the int to char, for example). In my case it gets confused between the various built-in operators and the ones I created. It seems to me like if I could flag the conversion operators as explicit somehow, that it would solve the issue, but as far as I can tell the explicit keyword is only for constructors (and I can't make constructors for built-in types). So is there any way of marking the casts as explicit? Or am I barking up the wrong tree here and there's another way of solving this? Or maybe I'm just doing something else wrong...

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