New to D and mimicking C++ : how to implement std::integral_constant<>?

[Picaud Vincent via Digitalmars-d-learn]

On Monday, 7 November 2016 at 18:59:24 UTC, Jerry wrote:
> On Monday, 7 November 2016 at 18:42:37 UTC, Picaud Vincent 
> wrote:
>> template isIntegralConstant(ANY)
>> {
>>     enum bool 
>> isIntegralConstant=__traits(identifier,ANY)=="IntegralConstant";
>> }
>
> A bit more elegant way of doing that would be:
>
> enum isIntegralConstant(T) = is(T : IntegralConstant!U, U...);
>
>
>> I would be very graceful for any help/advice that explains the 
>> right way to implement C++ std::integral_constant<T,T value> 
>> in the D language.
>>
>> Vincent
>
> Now the question is, do you really need IntegralConstant? I've 
> never used it in C++ so I don't really know any of the use 
> cases for it. But generally in D if you need something to be a 
> compile time constant value you can just use "enum". It can be 
> any type as well, so long as it can be evaluated at compile 
> time.
>
> enum long someConstant = 1 << 32;

Hi Jerry,

Thank you so much for your quick answer! I tried your suggestion 
and it works.

My main interest is numerical computations. I have some C++ libs 
using meta-programming and I want to see how I can translate some 
parts in D. The goal is to check: productivity & code readability 
& performance. I will try to implement 2 toy examples:

1/ A basic example of strided dense vector structure dealing with 
the dynamic/static size in an uniform way. In D I thing this can 
be done with something like this (not tried yet to compile it, 
but that is the idea to mimick my C++ implementation)

struct Vector(T,SIZE,STRIDE) if( 
(is(SIZE==size_t)||isIntegralConstant!SIZE) ...)
{
   alias T ElementType;

   private SIZE size_;
   private STRIDE stride_;

   ...

   auto required_capacity() { return size_*stride_; } // return a 
size_t or a IntegralConst

   static if ( isIntegralConstant!(typeof(required_capacity()) )
{
}
else
{
}

}