Constraints

[Chris Cain]

We can already kind of do what you're asking without a language 
feature. For instance, if you want to define that something is a 
type of range...

struct MyRange { ... }

static assert(isInputRange!MyRange); // won't compile unless 
MyRange is an input range

On Wednesday, 9 May 2012 at 15:04:51 UTC, İbrahim Gökhan 
YANIKLAR wrote:
> // implement foo's without constraints
> //------------------------------------------------------------
>
> void foo(Range)(Range r)
> 	if (isInputRange!Range && !isForwardRange!Range)
> { }
>
> void foo(Range)(Range r)
> 	if (isForwardRange!Range && !isBidirectionalRange!Range &&
> !isRandomAccessRange!Range)
> { }
>
> void foo(Range)(Range r)
> 	if (isBidirectionalRange!Range && !isRandomAccessRange!Range)
> { }
>
> void foo(Range)(Range r)
> 	if (isRandomAccessRange!Range)
> { }

And these could certainly use some library sugar. How about this:

template isJustInputRange(R) {
     enum bool isJustInputRange = isInputRange!R && 
!isForwardRange!R;
}

template isJustForwardRange(R) ...etc...