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generic and overloads.


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#1 slicer4ever   Crossbones+   -  Reputation: 3981

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Posted 14 July 2013 - 12:22 PM

having a bit of a problem with something i'd like to do in C#.  in c++ with templates it'd work, since the class would be compiled as w/e type it's being used for.  but in C# it seems that doesn't work in a similar manner.

 

here's what i'm trying to do: http://ideone.com/D6Tgke

 

using System;
namespace Main{
    
    class Test<T>{
        
        public Test(T Value){
            X.Foo(Value);
        }
    }
    
    
    class X{
        public static void Foo(int value){
            Console.WriteLine("Foo Int: "+value);
        }
        
        public static void Foo(float value){
            Console.WriteLine("Foo Float: "+value);
        }
        
        public static void Main(){
            Test<float> f = new Test<float>(5.0f);
            Test<int> i = new Test<int>(5);
            return;
        }
    }
}

 

which gives me the following errors:

 

prog.cs(7,15): error CS1502: The best overloaded method match for `Main.X.Foo(int)' has some invalid arguments
prog.cs(13,28): (Location of the symbol related to previous error)
prog.cs(7,15): error CS1503: Argument `#1' cannot convert `T' expression to type `int'
Compilation failed: 2 error(s), 0 warnings

any tips on what i could do to achieve this?


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#2 Nypyren   Crossbones+   -  Reputation: 4796

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Posted 14 July 2013 - 12:42 PM

C# generics are really cumbersome to use with value types.  As far as I know you have to move the type resolution from compile time to runtime. You could make an overload of X.Foo which takes an object and then calls the appropriate method using a series of "Value is Type" if/else statements. The easiest-to-implement hack I know of to get it to work is to use dynamic typing:
 
X.Foo((dynamic)Value);
Typically what I do instead is redesign the implementation so that the generic doesn't need to be used with value types. Sometimes this is pretty difficult, but often you will end up with code where the compiler is figuring everything out at compile time again, which is better.

#3 slicer4ever   Crossbones+   -  Reputation: 3981

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Posted 14 July 2013 - 12:53 PM

C# generics are really cumbersome to use with value types.  As far as I know you have to move the type resolution from compile time to runtime. You could make an overload of X.Foo which takes an object and then calls the appropriate method using a series of "Value is Type" if/else statements. The easiest-to-implement hack I know of to get it to work is to use dynamic typing:
 

X.Foo((dynamic)Value);
Typically what I do instead is redesign the implementation so that the generic doesn't need to be used with value types. Sometimes this is pretty difficult, but often you will end up with code where the compiler is figuring everything out at compile time again, which is better.

 

 

I see, that's unfortunate that c# can't do compile-time type detection for generics .  hmm, so my options are to type-cast to an object, and use reflection, or to simple create a unique instance of each type of class(which would be quite cumbersome...).

 

i suppose i'll use the type-cast mechanism for now, and so long as i don't see any terrible performance hit, i should be alright.

 

also, dynamic doesn't seem to be a known keyword for the c# compiler i'm using atm.


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#4 ChaosEngine   Crossbones+   -  Reputation: 2499

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Posted 14 July 2013 - 06:04 PM


I see, that's unfortunate that c# can't do compile-time type detection for generics .  

 

C# can absolutely do compile time type detection for generics (specifically method parameters). That's not what you're asking it to do with this code. You're looking for C++ style duck typing and expecting the code to be generated the same way it is for c++ templates. The two are very different.

 


 also, dynamic doesn't seem to be a known keyword for the c# compiler i'm using atm.

 

dynamic was introduced in .Net 4, I think. (VS2010)

 

Can you give a more concrete example of what you want to do? There may be better ways of solving the problem.


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#5 slicer4ever   Crossbones+   -  Reputation: 3981

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Posted 14 July 2013 - 07:04 PM

 


I see, that's unfortunate that c# can't do compile-time type detection for generics .  

 

C# can absolutely do compile time type detection for generics (specifically method parameters). That's not what you're asking it to do with this code. You're looking for C++ style duck typing and expecting the code to be generated the same way it is for c++ templates. The two are very different.

 

 


 also, dynamic doesn't seem to be a known keyword for the c# compiler i'm using atm.

 

dynamic was introduced in .Net 4, I think. (VS2010)

 

Can you give a more concrete example of what you want to do? There may be better ways of solving the problem.

 

the code i provided is a solid example.  i'm making an interface to PSM's shaderprogram, which has ~15 overloads of various uniform inputs(int's, floats, vector's, matrixs).  i created an material class, and then i can attach nodes to that material class(each node is a uniform, or a texture). the node has a uniform location/texture index, and a value(such as an int, float, vector, or matrix), and i use the generic to pass what type the value is suppose to be.  and then when i go to apply the value to the shader, i wanted it to choose the correct overload when passing the value into the shader.

 

i'm open to other possibilitys, but for now i'm simply using if-else branch to check the type.


Edited by slicer4ever, 14 July 2013 - 07:05 PM.

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