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digitalmars.D - Partial Specialization using Static If

reply Xinok <xnknet gmail.com> writes:
Going back to my 'multiple specialization' idea...

Static if can pretty much do the job of multiple specialization, except for
one case: partial specialization.

template temp(T : T*)

This doesn't work in a static if:
static if(is(T == T*))
Assuming T = int, the compiler would read this as:
static if(is(int == int*))


I'll forget about the multiple specialization idea for now. We need a simple
way to do partial specialization in a static if expression. It is possible to
do using a specialized template, but it's a bit of work.

template IsPtr(T){
	const bool IsPtr = false;
}
template IsPtr(T : T*){
	const bool IsPtr = true;
}

template temp(T1, T2, T3){
	static if(IsPtr!(T1) || IsPtr!(T2) || IsPtr(T3)){
	}
}
Dec 24 2006
parent Kirk McDonald <kirklin.mcdonald gmail.com> writes:
Xinok wrote:
 Going back to my 'multiple specialization' idea...
 
 Static if can pretty much do the job of multiple specialization, except for
 one case: partial specialization.
 
 template temp(T : T*)
 
 This doesn't work in a static if:
 static if(is(T == T*))
 Assuming T = int, the compiler would read this as:
 static if(is(int == int*))
 

But you can say this: static if (is(T U == U*)) U is then declared to be an alias of the type T is a pointer to (and it only exists within the static if's scope). Assuming T is int*, you get static if (is(int* U == int*)) static assert(is(U == int)); This works more generally, too: static if (is(T U == U[])) That determines if T is a dynamic array, and U becomes an alias for the type of an element of the array.
 
 I'll forget about the multiple specialization idea for now. We need a simple
 way to do partial specialization in a static if expression. It is possible to
 do using a specialized template, but it's a bit of work.
 
 template IsPtr(T){
 	const bool IsPtr = false;
 }
 template IsPtr(T : T*){
 	const bool IsPtr = true;
 }
 
 template temp(T1, T2, T3){
 	static if(IsPtr!(T1) || IsPtr!(T2) || IsPtr(T3)){
 	}
 }

-- Kirk McDonald Pyd: Wrapping Python with D http://pyd.dsource.org
Dec 24 2006