To solve the problem of converting a Object to a specific template class i wrote this little function.
But the mixin disturbs me. How i can get the type (in this example Vector2D) without to mix a mixin and T.stringof?

[code]
T object_cast(T : Object)(Object value) {
	T val = cast(T) value;
	
	if (val !is null) {
		return val;
	}
	
	// if cast fails it is a template class
	
	import std.typetuple;
	
	foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int, uint, long, ulong, float, double, real)) {
		mixin("
		if (auto vec = cast(" ~ T.stringof ~ "!(" ~ Type.stringof ~ "))(value)) {
			return cast(T) vec;
		}");
	}
	
	return null;
}
[/code]

On Thursday, 21 June 2012 at 10:33:41 UTC, Namespace wrote:
> To solve the problem of converting a Object to a specific template class i wrote this little function.
> But the mixin disturbs me. How i can get the type (in this example Vector2D) without to mix a mixin and T.stringof?
>
> [code]
> T object_cast(T : Object)(Object value) {
> 	T val = cast(T) value;
> 	
> 	if (val !is null) {
> 		return val;
> 	}
> 	
> 	// if cast fails it is a template class
> 	
> 	import std.typetuple;
> 	
> 	foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int, uint, long, ulong, float, double, real)) {
> 		mixin("
> 		if (auto vec = cast(" ~ T.stringof ~ "!(" ~ Type.stringof ~ "))(value)) {
> 			return cast(T) vec;
> 		}");
> 	}
> 	
> 	return null;
> }
> [/code]

If you use 2.060head (git version), you can get template from the instantiated type.

class Vec(T) {}

void main()
{
    alias Vec!int IntVec;
    static if (is(IntVec _unused : V!T, alias V, T))
    {
        // V is class template Vec
        alias V!double DoubleVec;  // another type instantiation test
        static assert(is(DoubleVec == Vec!double));  // equal!
    }
    else
        static assert(0);
}

Works in dmd  2.059 too.

[code]
T template_cast(T : Object, U : Object)(U value) {
	// try to convert
	T val = cast(T) value;
	
	// if convert was successful, return
	if (val !is null) {
		return val;
	}
	
	// if cast fails it is a template class
    static if (is(T ClassType : V!W, alias V, W)) {
        // V is the template class
		import std.typetuple;
		
		// find out which one is "value"'s original type
		foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int, uint, long, ulong, float, double, real)) {
			// if found: cast
			writeln(Type.stringof);
			if (auto vec = cast(V!Type) value) {
				return cast(Unqual!T) vec;
			}
		}
		
		return null;
    } else {
		return null;
	}
}
[/code]

Example:
[code]
class Rect(T) {
	T opCast(T : inout(Rect!U), U)() inout {
		return new T();
	}
	
	override string toString() const {
		return "Rect!(" ~ T.stringof ~ ")";
	}
}

void foo(Object o) {
	write("O ist: ");
	writeln(o);
	
	write("self cast: ");
	writeln(cast(Rect!int) o);
	
	write("template cast: ");
	Rect!int ri = template_cast!(Rect!int)(o);
	
	write("Result: ");
	writeln(ri);
}

Rect!(float) rf = new Rect!(float)();

foo(rf);
[/code]

On Thursday, 21 June 2012 at 21:32:57 UTC, Namespace wrote:
> Works in dmd  2.059 too.

Oh, good.

> [code]
> T template_cast(T : Object, U : Object)(U value) {
> 	// try to convert
> 	T val = cast(T) value;
> 	
> 	// if convert was successful, return
> 	if (val !is null) {
> 		return val;
> 	}
> 	
> 	// if cast fails it is a template class
>     static if (is(T ClassType : V!W, alias V, W)) {
>         // V is the template class
> 		import std.typetuple;
> 		
> 		// find out which one is "value"'s original type
> 		foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int, uint, long, ulong, float, double, real)) {
> 			// if found: cast
> 			writeln(Type.stringof);
> 			if (auto vec = cast(V!Type) value) {
> 				return cast(Unqual!T) vec;
> 			}
> 		}
> 		
> 		return null;
>     } else {
> 		return null;
> 	}
> }
> [/code]
>
> Example:
> [code]
> class Rect(T) {
> 	T opCast(T : inout(Rect!U), U)() inout {
> 		return new T();
> 	}
> 	
> 	override string toString() const {
> 		return "Rect!(" ~ T.stringof ~ ")";
> 	}
> }
>
> void foo(Object o) {
> 	write("O ist: ");
> 	writeln(o);
> 	
> 	write("self cast: ");
> 	writeln(cast(Rect!int) o);
> 	
> 	write("template cast: ");
> 	Rect!int ri = template_cast!(Rect!int)(o);
> 	
> 	write("Result: ");
> 	writeln(ri);
> }
>
> Rect!(float) rf = new Rect!(float)();
>
> foo(rf);
> [/code]

Seems to me that you achieved the your first purpose. Do you need more help?

Kenji Hara

> Seems to me that you achieved the your first purpose. Do you need more help?
>
> Kenji Hara

I think i'm finished. Or have you any tip for me, related to the code?