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Template Functions?


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#1 bollµ   Members   -  Reputation: 354

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Posted 13 December 2012 - 07:08 AM

Hi all!

I've been binding angelscript with my game engine. So far, it's been smooth sailing. lovely scripting language! Posted Image

I'd like to be able to bind a function that returns a variable type. (A template function basically)

The function is this one:

template<typename T>
T getAttribute(const char *element){

  static char attribute[1024];
  static std::stringstream strStream;

  memset(attribute, 0, 1024);
  strStream.clear();

  this->getAttribute(element, attribute);
  strStream<<attribute;

  T value;
  strStream>>value;

  return value;
};

Is there any way to bind this function? I've read through the docs and I didn't really see anything.

Is there anything I can do to make this work? (I don't want to change the class itself. I'd be okay writing a wrapper around that method)
(or) can I use CScriptAny in some way to store and return the data I need?

The datatypes that I'll be returning are usually int, float, double or string (I'm using the CScriptString extension).

Thanks all!

a WIP 2d game engine: https://code.google.com/p/modulusengine/

English is not my first language, so do feel free to correct me :)


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#2 Andreas Jonsson   Moderators   -  Reputation: 3444

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Posted 13 December 2012 - 08:16 AM

Templates in C++ doesn't exist until the type that will be used is defined. As the template arg only changes the return type, you will not be able to register it multiple times for the different types you wish to support. So your only option is to use wrappers. There are basically two alternatives that I can think of:

1) You can write the wrapper to return a CScriptAny, which would allow the function to return any value. If you don't know at compile time which types needs to be supported, then this is what you need to use.

2) Register multiple wrappers that return the value in an output reference. The latter is probably easier to implement and also more intuitive for the script writers to use. The wrappers can be implemented like this:

void getAttributeWrap(const std::string &name, int &retValue)
{
  retValue = getAttribute<int>(name.c_str());
}

The wrapper is registered as RegisterGlobalFunction("void getAttribute(const string &in, int &out)", asFUNCTIONPR(getAttributeWrap, (const std::string &in, int &), void), asCALL_CDECL);

The wrapper itself can be a template implementation so you don't need to write the code multiple times. You still need to register it for each type you want to support though.

Regards,
Andreas
AngelCode.com - game development and more - Reference DB - game developer references
AngelScript - free scripting library - BMFont - free bitmap font generator - Tower - free puzzle game

#3 bollµ   Members   -  Reputation: 354

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Posted 14 December 2012 - 06:45 AM

well, the function belongs to a class, so I'm guessing I can also bind it as a member function using this technique can't I?

It is also possible to register a global function that takes a pointer to the object as a class method. This can be used to extend the functionality of a class when accessed via AngelScript, without actually changing the C++ implementation of the class.
// Register a global function as an object method
void MyClass_MethodWrapper(MyClass *obj)
{
// Access the object
obj->DoSomething();
}
r = engine->RegisterObjectMethod("mytype", "void MethodWrapper()", asFUNCTION(MyClass_MethodWrapper), asCALL_CDECL_OBJLAST); assert( r >= 0 );

I don't really have time today, so I'll implement it tomorrow. I hadn't thought of the second way at all. it sounds like a really nice solution. thanks! :)

also, <3 Angelscript

a WIP 2d game engine: https://code.google.com/p/modulusengine/

English is not my first language, so do feel free to correct me :)


#4 Andreas Jonsson   Moderators   -  Reputation: 3444

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Posted 14 December 2012 - 08:19 AM

Yes. The same technique can be used for class methods too.

The asCALL_CDECL_OBJLAST/OBJFIRST exist exactly for the reason you mentioned, to extend a registered class without modifying the class itself. :)
AngelCode.com - game development and more - Reference DB - game developer references
AngelScript - free scripting library - BMFont - free bitmap font generator - Tower - free puzzle game




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