[Issue 6221] Should be possible to pass struct function returns by 'const ref'.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6221



--- Comment #2 from Don <clugdbug at yahoo.com.au> 2011-06-29 23:54:17 PDT ---
(In reply to comment #1)
> I think this bug is invalid.  A value-type return is an rvalue, and Andrei has
> made it very clear in his posts and in TDPL that rvalues cannot be bound to
> const ref parameters.  I think his reasoning is that this ability was a mistake
> in C++, though I haven't gotten consistent answers as to why.

That's probably true. But that has consequences. We can't discard that C++
behaviour and yet keep the C++ behaviour of using const ref in operator
overloads:

> The fact that it works with opCmp in one direction is I think a relaxation of
> the rules, because struct returns would be near useless if you couldn't call
> any methods on them.

This is a serious problem. opCmp behaviour MUST be symmetrical.

S foo() {...}
S x;

  x > foo()
  foo() < x
  foo() > foo()

If any of these compile, they must all compile.

As far as I can tell, a 'const ref' parameter on pretty much any operator
overload, is a bug. In fact it's difficult to come up with _any_ scenarios
where 'const ref' makes sense.

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