Daniel Walker wrote:
On 4/27/07, Peter Dimov <pdimov@mmltd.net> wrote:
Yes, this is one of the reasons why boost::bind( ... ) == 5 is valid, but _1 == 5 is not (the other being that given placeholder interoperability, both Bind and Lambda will claim _1 == 5 as their own.)
Right. As long as lambda has it's own placeholders you'll need to disambiguate them with namespace qualification or using directives.
No, this wasn't what I had in mind. Consider what would happen if boost::bind supplies a "proper" operator==( a, b ) that attempts to return bind<bool>( __equal_to(), a, b ) and makes it work not just when a or b is a bind() expression (as is the case today), but for placeholders as well. Lambda also has its operator== which does a similar thing, except that it returns a lambda object. If Lambda starts recognizing Bind's placeholders as its own, the two operator== overloads (if visible) will both match ::_1 == 5. A similar ambiguity would occur with ll::_1 == 5 if Bind recognizes ll::_1 as a placeholder (which it already does).