WAT: opCmp and opEquals woes

[H. S. Teoh via Digitalmars-d]

On Fri, Jul 25, 2014 at 02:05:13PM -0700, Walter Bright via Digitalmars-d wrote:
> On 7/25/2014 12:03 PM, "Marc Schütz" <schuetzm at gmx.net>" wrote:
> >No, if a type had only defined opCmp because of the previous AA
> >(mis)implementation,
> 
> It was not a misimplementation. The previous implementation used a
> hash lookup with a binary tree for collisions, hence it needed cmp. It
> was perfectly correct. The newer one uses a linear list for
> collisions, hence it only needs ==.

So it sounds like Jonathan's solution is the best after all: get rid of
the error message that demands that opEquals be defined when opCmp is
defined.  Previous code that defined opCmp for AA keys will then
continue to work (except if their opCmp was inconsistent with the
default opEquals, in which case they are already buggy and we're not
making things worse).

On a related note, it would be nice if AA key types that did define
opCmp can have better than linear collision resolution. But that belongs
in another discussion.

On another related note, the compiler's treatment of opCmp is
inconsistent:

	struct S {
		int opCmp(S s) { return 0; }
	}
	int[S] aa1;	// OK

	struct T {
		int opCmp(T s) const { return 0; }
	}
	int[T] aa2;	// Compile error: must also define opEquals

Worse yet:

	struct S
	{
		int x;
		int opCmp(S s) /*const*/ {
			return s.x - x;
		}
	}

	void main() {
		auto s1 = S(1);
		auto s2 = S(2);

		assert(s1 > s2);
		assert(s2 < s1);

		assert(typeid(s1).compare(&s1, &s2) > 0);
		assert(typeid(s2).compare(&s2, &s1) < 0);
	}

This produces a runtime error:

	object.Error@(0): TypeInfo.compare is not implemented

Uncommenting the const in opCmp fixes the problem.  WAT?


T

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