[RFC] std.experimental.concepts

[Martin Nowak via Digitalmars-d]

On Saturday, 25 July 2015 at 14:06:05 UTC, Daniel N wrote:
> On Friday, 24 July 2015 at 19:56:55 UTC, Shammah Chancellor 
> wrote:
>> I put up a PR for phobos awhile ago for concepts as a library 
>> to kind of start the discussion around concepts.   There 
>> seemed to be some interest around the PR, so I have rebased it 
>> and fixed the formatting.
>>
>> Please take a look: 
>> https://github.com/D-Programming-Language/phobos/pull/2627
>>
>> -Shammah
>
> For those who are on a sugar-rush from Concepts, maybe this is 
> a fun trick?
>
> It almost works, if only IFTI was smart enough to deal with 
> eponymous identity templates.
>
> ========================================
> int fun(T)(T t) if(is(typeof(T.Put)))
> {
> }
> ========================================
> template Putty(T)
> {
>   static assert(is(typeof(T.Put)));
>
>   alias Putty = T;
> }
> void fun(T)(Putty!T t)
> {
> }
> ========================================

Templates are not bijective, so we'll never be generally able to 
determine T by matching Putty, i.e. 2 different T could have the 
same Putty!T type.
Adding an exception for identity templates seems to be a hack.