Re: DIP58: ".." as a Binary Operator

[Mason McGill]

Random thought, but treating step as a template argument would 
allow for some more interesting changes to the iterations, 
though I can't think of any particular syntax that would look 
good. And if you did add such a thing, then other operators 
would want it as well.

Interesting, though I feel like operator syntax really shines 
when either
  1) It's significantly shorter/simpler than the equivalent 
function calls.
  2) It appeals to domain-specific intuitions.
In terms of (1) and (2), I think better spellings for these might 
be

int[] foo = a ..!"a += 10" b;

import std.array: array;
import std.range: iota;

int[] foo = array(iota(a, b, 10));
// Or something with recurrence, in the general case.

bool equals = dbl1 ==."abs(a - b) < 0.01" dbl2

import std.math: abs;

struct Approximation(A)
{
    A a;
    alias a this;

    bool opEquals(B)(B b) const
      { return abs(a - b) < 0.01; }
}

auto approximate(A)(A a)
  { return Approximation!A(a); }

bool equals = approximate(a) == b;