++Phobos

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On Friday, 18 October 2019 at 00:19:08 UTC, rikki cattermole 
wrote:
>> Correct me if I'm wrong, but would using this with std.range 
>> be as simple as:
>> 
>> import std.range;
>> 
>> @implements!(MyCoolRange, InputRange)
>> struct MyCoolRange(T)
>> {
>>      ....
>> }
>> 
>> long sum(R)(R range)
>> if (implements!(R, InputRange))
>> {
>>      ....
>> }
>
> This unfortunately still ties the implementation itself to the 
> interface. Which goes against DbI.

Not necessarily. I haven't tried this myself, but I think you 
could get pretty far with UDAs and some template magic. What I'm 
thinking:

//Unfortunately this is necessary so that R is in scope for the 
UDAs.
//Maybe it can be avoided with std.traits.TemplateArgsOf / 
TemplateOf?
template MapResult(R)
{
     //MapResult is always at least an input range
     @implements!(MapResult, InputRange)

     //If the wrapped type is a forward range, MapResult
     //is also a forward range and will forward to its 
implementation
     @given!(implements!(R, ForwardRange),
             implements!(inheritImpl!(ForwardRange, MapResult, R), 
ForwardRange))

     //etc.
     struct MapResult
     {
         R store;

         mixin forwardTo!(ForwardRange, store);

         //Input range primitives defined down here
     }
}