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Subject: Re: [boost] [TypeTraits] propose new callable-type call traits
From: TONGARI J (tongari95_at_[hidden])
Date: 2014-01-11 14:55:23


2014/1/12 Hui Li <hui.li_at_[hidden]>

> I've implemented a few traits classes (code attached below) that, for a
> given callable-type T, and a set of Args..., detects whether the function
> call T::operator()(Args...) would be
> (1) valid,
> (2) ambiguous, or
> (3) none is viable.
> where T is allowed to have arbitrary overloaded operator()'s.
> This could be useful for programmers who want to
> (1) make the function call only when it's valid,
> (2) generate customized error/warning messages when it's ambiguous, or
> handle/redirect it without getting an ambiguous compiler error, and
> (3) redirect non-viable calls to some default behavior, which can be
> different than how it's handled when the call is ambiguous.
> If people are interested, I suppose this could be a useful addition to
> TypeTraits.
> I would appreciate any feedback!
> For clarity, the implementation and demonstration attached below is
> written in c++11. It can be easily ported to c++98/03 compilers by using
> TypeTratis to replace the std type traits, BOOST_TYPEOF_KEYWORD to replace
> decltype, and Boost.Preprocessor to generate code for arbitrary arity.

It's interesting that you use ambiguity to distinguish the types.
Anyway, your code doesn't support function(pointer) which is also Callable,
and... are you sure your approach can be ported back to C++03 where there's
no SFINAE on expression?

FWIW, I have my has_call implementation:
which works for both C++11/03.

I have real world usage of has_call (or has_valid_call in yours), but I
don't have the need of has_ambiguous_call so far.

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