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

[Biotronic via Digitalmars-d]

On Thursday, 30 July 2015 at 10:40:59 UTC, Atila Neves wrote:
There's still the problem of having two names for each 
constraint: checkInputRange and isInputRange. But... we could 
also establish the convention of checkXXX and use string mixins 
to turn this:

@satifies!(isInputRange, MyRange)

into (which works cos I just tried it):

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)"
}


@satisfies!(isInputRange, Zeroes)
struct Zeroes {
    enum empty = false;
    void popFront() {}
    @property int front() { return 0; }
}


Now, _this_ I could go for.

Atila

Why are there two different things in the first place?

@satisfies!(myConcept, T) should test the constraints and give a 
sensible error message. This you use to indicate that type T 
implements myConcept.

Why can't another template use the very same concept information 
to check if a type implements the concept?

e.g.:

@satisfies!(myConcept, MyStruct)
struct MyStruct { /* ... */ }

void foo(T)(T t) if (check!(myConcept, T))
{ /* ... */ }