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SFINAE-fail mp_eval_if when F<U...> is invalid

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This commit is contained in:
Peter Dimov
2017-05-18 15:22:05 +03:00
parent 37bbb15375
commit 611ea810bd
3 changed files with 55 additions and 21 deletions
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41
include/boost/mp11/utility.hpp
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@@ -52,27 +52,6 @@ template<class T, class E> struct mp_if_c_impl<false, T, E>
template<bool C, class T, class... E> using mp_if_c = typename detail::mp_if_c_impl<C, T, E...>::type;
template<class C, class T, class... E> using mp_if = typename detail::mp_if_c_impl<static_cast<bool>(C::value), T, E...>::type;
// mp_eval_if, mp_eval_if_c
namespace detail
{
template<bool C, class T, template<class...> class F, class... U> struct mp_eval_if_c_impl;
template<class T, template<class...> class F, class... U> struct mp_eval_if_c_impl<true, T, F, U...>
{
using type = T;
};
template<class T, template<class...> class F, class... U> struct mp_eval_if_c_impl<false, T, F, U...>
{
using type = F<U...>;
};
} // namespace detail
template<bool C, class T, template<class...> class F, class... U> using mp_eval_if_c = typename detail::mp_eval_if_c_impl<C, T, F, U...>::type;
template<class C, class T, template<class...> class F, class... U> using mp_eval_if = typename detail::mp_eval_if_c_impl<static_cast<bool>(C::value), T, F, U...>::type;
// mp_valid
// implementation by Bruno Dutra (by the name is_evaluable)
namespace detail
@@ -107,6 +86,26 @@ struct mp_no_type
template<template<class...> class F, class... T> using mp_defer = mp_if<mp_valid<F, T...>, detail::mp_defer_impl<F, T...>, detail::mp_no_type>;
// mp_eval_if, mp_eval_if_c
namespace detail
{
template<bool C, class T, template<class...> class F, class... U> struct mp_eval_if_c_impl;
template<class T, template<class...> class F, class... U> struct mp_eval_if_c_impl<true, T, F, U...>
{
using type = T;
};
template<class T, template<class...> class F, class... U> struct mp_eval_if_c_impl<false, T, F, U...>: mp_defer<F, U...>
{
};
} // namespace detail
template<bool C, class T, template<class...> class F, class... U> using mp_eval_if_c = typename detail::mp_eval_if_c_impl<C, T, F, U...>::type;
template<class C, class T, template<class...> class F, class... U> using mp_eval_if = typename detail::mp_eval_if_c_impl<static_cast<bool>(C::value), T, F, U...>::type;
// mp_quote
template<template<class...> class F> struct mp_quote
{

1
test/Jamfile.v2
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@@ -77,6 +77,7 @@ run mp_inherit.cpp : : : $(REQ) ;
run mp_if.cpp : : : $(REQ) ;
run mp_if_sf.cpp : : : $(REQ) ;
run mp_eval_if.cpp : : : $(REQ) ;
run mp_eval_if_sf.cpp : : : $(REQ) ;
run mp_valid.cpp : : : $(REQ) ;
run mp_defer.cpp : : : $(REQ) ;
run mp_quote.cpp : : : $(REQ) ;

34
test/mp_eval_if_sf.cpp Normal file
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@@ -0,0 +1,34 @@
// Copyright 2017 Peter Dimov.
//
// Distributed under the Boost Software License, Version 1.0.
//
// See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt
#include <boost/mp11/utility.hpp>
#include <boost/core/lightweight_test_trait.hpp>
#include <type_traits>
using boost::mp11::mp_eval_if;
using boost::mp11::mp_identity_t;
template<class C, class... A> using eval_if = mp_eval_if<C, void, mp_identity_t, A...>;
int main()
{
using boost::mp11::mp_valid;
BOOST_TEST_TRAIT_TRUE((mp_valid<eval_if, std::true_type>));
BOOST_TEST_TRAIT_TRUE((mp_valid<eval_if, std::true_type, void>));
BOOST_TEST_TRAIT_TRUE((mp_valid<eval_if, std::true_type, void, void>));
BOOST_TEST_TRAIT_TRUE((mp_valid<eval_if, std::true_type, void, void, void>));
BOOST_TEST_TRAIT_FALSE((mp_valid<eval_if, std::false_type>));
BOOST_TEST_TRAIT_TRUE((mp_valid<eval_if, std::false_type, void>));
BOOST_TEST_TRAIT_FALSE((mp_valid<eval_if, std::false_type, void, void>));
BOOST_TEST_TRAIT_FALSE((mp_valid<eval_if, std::false_type, void, void, void>));
return boost::report_errors();
}