concepts

[extrawurst via Digitalmars-d]

On Thursday, 21 May 2015 at 08:17:47 UTC, Vlad Levenfeld wrote:
> How possible is something like this:
>
>   auto foo (T)(T t)
>   if (is(Eq!T) && is(Num!T) && T.sizeof == 4)
>   {...}
>
>   foo ("hello");
>
> then you get some output from the compiler, something like
>
>   Error: template foo cannot deduce function from argument 
> types !()(string),
>   candidates are:
>
>     foo(T)(T x)
>     pass is(Eq!T)
>     fail is(Num!T)
>     fail T.sizeof == 4
>
> Since template code (and by extension its constraint) is known 
> to the compiler, would it break anything to have it parse the 
> logical connectives and state specifically what fails for each 
> attempted match?

that would be great!