Howard Hinnant wrote:
On Nov 30, 2004, at 7:52 AM, David Abrahams wrote:
Peter Dimov wrote:
David Abrahams wrote:
Peter Dimov wrote:
(I had boost::placeholders in mind for a namespace, consistent with std::tr1::placeholders; when you use 'boost' as a substitute for 'std::tr1', boost::bind::placeholders won't work.)
Okay, as long as you cooperate with phoenix and lambda, as far as I'm concerned. What specific kind of cooperation do you have in mind?
Ideally? You all use the same placeholders.
I've also wondered if a general "placeholder library" is possible.
It's possible to write libraries so that they recognize the same placeholders, but the existing Bind and Lambda codebases aren't written in such a way. However I'd expect Metrowerks's implementation to be able to use Bind's and Lambda's placeholders; the only thing that is needed is appropriate specializations of std::tr1::is_placeholder. By specializing std::tr1::is_bind_expression for boost::_bi::bind_t<R, F, L>, std::tr1::bind should even be able to recognize a nested boost::bind subexpression. Daniel Wallin's suggestion of using #define _1 arg<1>() which is both a type and a value can enable even type (mpl) and value (bind, lambda) placeholders to be unified. Of course I can only imagine what the response to a macro _1 would be from an audience that can't even stand a global _1.