Interfaces, traits, concepts, and my idea for a DIP

[Piotrek via Digitalmars-d]

On Friday, 31 July 2015 at 16:28:30 UTC, jmh530 wrote:
> Looking at the PR also resolved my earlier question. Running 
> the code as below (do not import std.range) will tell you 
> exactly what isn't implemented from isInputRange (in this case, 
> I commented out popFront). Very cool.
>
> template satisfies(alias Constraint, R) {
>     enum check = "check" ~ Constraint.stringof[2..$-3] ~ "!(R)";
>     enum assert_ = "static assert("~ check ~ ");";
>     mixin(assert_); //mixes in "static 
> assert(checkInputRange!R)"
> }
>
> template isInputRange(R)
> {
>     enum bool isInputRange = is(typeof(checkInputRange!R));
> }
>
> bool checkInputRange(R)(inout int = 0)
> {
>     if (__ctfe)
>     {
>         R r = R.init;     // can define a range object
>         if (r.empty) {}   // can test for empty
>         r.popFront();     // can invoke popFront()
>         auto h = r.front; // can get the front of the range
>     }
>     return true;
> }
>
> @satisfies!(isInputRange, Zeroes)
> struct Zeroes {
>     enum empty = false;
>     //void popFront() {}
>     @property int front() { return 0; }
> }
>
> void main()
> {
> 	Zeroes Z;
> }

Nice. Here are the actual error messages for the record:

/d125/f236.d(18): Error: no property 'popFront' for type 'Zeroes'
/d125/f236.d(24): Error: template instance 
f236.satisfies!(isInputRange, Zeroes) error instantiating

Piotrek