RFC: Change operator method lookup to be less magical

[nikomatsakis]

Right now, operator "methods" proceed according to the same logic as any other method. But this leads to surprising results like this: https://gist.github.com/bstrie/4948410

Also, operators are already handled somewhat specially because we auto-ref their arguments. This means that you can write val1-of-my-linear-type == val2-of-my-linear-type and it doesn't move or do anything creepy (to call eq explicitly, in contrast, you'd write val1-of-my-linear-type.eq(&val2-of-my-linear-type)).

I think method lookup for operators should never apply any automatic transformations to the receiver or arguments, other than the current auto-ref behavior (which means that a OP b is kind of implicitly (&a).OP(&b))

@pcwalton I expect you in particular might have an opinion about this.

[nikomatsakis]

I think this should apply also to unary operators and the [] operator, except that [] autoderefs its receiver (as it does normally).

[nikomatsakis]

Discussed in meeting: https://github.com/mozilla/rust/wiki/Meeting-weekly-2013-03-12

[nikomatsakis]

It seems that we only partially discussed this issue in the meeting. In particular, we did not discuss:

1. Removing argument coercions from uses of overloaded operators
2. Extending auto-ref to the argument of the [] operator, which seems useful for hashtables

On point 2, currently a[b] is converted to a.index(b) but if we extended autoref (as we do with all other operators) it would be equivalent to a.index(&b).

[graydon]

seems reasonable to me

[graydon]

Looks like this was merged in #5558 .. @nikomatsakis can this close?

[pnkfelix]

Visiting for triage, email from 2013-09-02.

Nominating for milestone 1, well-defined.

(Of course, its possible that graydon's hypothesis that this might be closeable is true. @nikomatsakis, any thoughts?)

[nikomatsakis]

Not closeable in that point 1 remains unresolved: do we want to coerce arguments? I remember @pcwalton had this on the agenda recently (under the guise of == operations).

[catamorphism]

Accepted for milestone 1, well-defined

[flaper87]

Triage bump, this still needs some work.