Daniel Walker wrote:
On 4/27/07, Peter Dimov <pdimov@mmltd.net> wrote:
Daniel Walker wrote:
[...]
_1 == _2 // ambiguous lambda::hold(_1) == _2 // lambda expression lambda::release(_1) == _2 // 3rd-party expression
I think that the right thing here (if we take the interoperability issue to heart) is to make
_1 == _2
"just work". It's an interesting challenge, but it's not impossible since that is exactly what is_bind_expression is intended to solve.
OK, I think you're bring up something new here with is_bind_expression that I haven't thought of yet. But first back to placeholders. _1 == _2 will "just work" as long as lambda is the only party overloading operator==.
It won't if you haven't included a lambda header or if you're using a compiler that is supported by Bind, but not by Lambda. The idea of "just works" is that _1 == _2 for Bind placeholders should be resolved by Bind without an ambiguity, yet it should still be recognized by Lambda as a subexpression. _1 + _2, however, should be picked up by Lambda because Bind does not support operator+, only relations and logical not.