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To: gcc@gcc.gnu.org
From: Larry Evans <cppljevans@suddenlink.net>
Subject: Re: optimization question: mpl
Date: Wed, 28 Jul 2010 17:26:00 -0000
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On 07/28/10 10:53, Hite, Christopher wrote:
[snip]
> struct DecodeContext;
> 
> struct M1{
> 	static const int id=1;
> 	static void decode(DecodeContext& ){}
> };
> 
> struct M2{
> 	static const int id=2;
> 	static void decode(DecodeContext& ){}
> };
> 
> struct M3{
> 	static const int id=3;
> 	static void decode(DecodeContext& ){}
> };
> 
> 
> template <int> struct ListMember;
> 
> template <> struct ListMember<1>{ typedef M1 type; };
> template <> struct ListMember<2>{ typedef M2 type; };
> template <> struct ListMember<3>{ typedef M3 type; };
> 
> template<int i>
> void foo(int id, DecodeContext& dc) {
> 	typedef typename ListMember<i>::type M;
> 	if(M::id==id)
> 		M::decode(dc);
> 	else
> 		foo<i-1>(id,dc);
> }
> 
> template<>
> void foo<0>(int id, DecodeContext& dc) {}
> 
> 
> 
> int main(){
> 	DecodeContext& dc= *(DecodeContext*)0;// junk for now
> 	int id=2; //sometime runtime dependent
> 	foo<3>(id,dc);
> 	return 0;
> }
> 
[snip]
Wouldn't the following simplification work just as well?

template <int Id> struct ListMember{
         static void decode(DecodeContext& ){}
};

template<int i>
void foo(int id, DecodeContext& dc) {
	if(i=id)
                 ListMember<i>::decode(dc);
	else
                 foo<i-1>(id,dc);
}