Re: [Boost-users] [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

Daniel Wallin writes:

JOAQUIN LOPEZ MU?Z wrote:

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I've read this over and over and can't say whether you're correcting Dave or me :( excuse my incompetence. So, given (in the context of class template parameters)

requiredtag::T,F>,

can Boost.Parameter match it to T<X> even if X does *not* satisfy F? Thank you!

Yes, that is correct. However, is you use `parameters::match<>` to restrict a function template, SFINAE will kick in. For example:

BOOST_PARAMETER_FUNCTION((void), f, tag, (deduced (required (x, (std::string))) ) );

f(x = 10); // no overload matches

OK, thanks for the info! Since it's only class templates that I'm interested, the behavior is exactly what I need. In the meantine, I've tried the lib and learnt the additional fact that, for requiredtag::T,F>, if T<X> is passed and T<X> (rather than X) satisfies F, then Boost.Parameter returns X as the matched arg rather than T<X>. Not that this poses any particular difficulty with what I'm trying to use the lib for, but it's a somewhat corner case I'd like to share with you. BTW, Boost.Parameter is a pleasure to work with! I hope to be able to show soon a B.P-powered lib where your stuff makes it a joy, both for the lib writer and the user, to deal with class templates with lots of parameters. Best, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo