Problem about Tuple.opEquals, const qualifier

[Tongzhou Li]

On Sunday, 18 March 2012 at 06:15:16 UTC, Ali Çehreli wrote:
> Every template instantiation of a set of template parameters 
> becomes a distinct type than any other set of template 
> parameters.
>
> In other words, Tuple!(double, char) and Tuple!(int, char) are 
> distinct types. For all the compiler knows, Tuple is a user 
> type and only the user should define whether they are 
> compatible. Tuple does not define opCast() to covert from 
> Tuple!(int,char) to Tuple!(double,char). I guess it could have 
> been defined. (?)
>
> A solution is to explicitly perform the conversion:
>
> import std.conv;
> // ...
>     stack ~= to!(Tuple!(double, char))(tuple(10, '+'));
>
> (An alias would make that easier to read. :/).
It seems long and ugly...
I also write:
     Tuple!(uint, double delegate(double, double))[char] Operators;
     Operators['+'] = tuple(1u, (x, y) => x + y);
It doesn't work. I have to write:
     Operators['+'] = tuple(1u, cast(double delegate(double, 
double))(x, y) => x + y);
Much longer :/

Someone tell me that this is called SFINAE problem in C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2634.html
I tried this C++ code:
     stack<pair<double, char> > s;
     s.push(make_pair(10, '+'));
It compiles fine with g++.
Any chance to see this being solved in D?
;)