Re: [boost] Mixing protocol

Subject: Re: [boost] Mixing protocol
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-01-15 14:35:04

AMDG

Joel Falcou wrote:
> So far BOOST proposes various prtocols for meta-function :
>
> - the result_of protocol
> - the apply<> protocol of MPL
> - the ::type protocol of traits
>
> Can those protocols be mixed somehow without any side-effects when used
> with the various aforementionned protocol ?

What do you mean by mixed?

result_of looks for a nested result or result_type only.  It is
unaffected by apply/type.

MPL uses both apply and type and also has a metafunction called apply:

struct identity {
    template<class T>
    struct apply {
        typedef T type;
    };
};

typedef mpl::apply<identity, int>::type int_;

boost::mpl::apply is generally preferable, because it works
with MPL Lambda expressions as well as metafunction classes.

In Christ,
Steven Watanabe