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Add indirection in mp_quote to enable expansions of T... into a fixed parameter list

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This commit is contained in:
Peter Dimov
2017-03-20 16:55:00 +02:00
parent 71ba80d18a
commit 321a54728f
3 changed files with 23 additions and 6 deletions
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11
include/boost/mp11/utility.hpp
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@@ -106,7 +106,16 @@ template<template<class...> class F, class... T> using mp_defer = mp_if<mp_valid
// mp_quote // mp_quote
template<template<class...> class F, class... T> struct mp_quote template<template<class...> class F, class... T> struct mp_quote
{ {
template<class... U> using fn = F<T..., U...>; private:
template<class... U> struct _fn { using type = F<T..., U...>; };
public:
// the indirection through _fn works around the language inability
// to expand T.. to expand into a fixed parameter list of an alias template
template<class... U> using fn = typename _fn<U...>::type;
}; };
// mp_unquote // mp_unquote

7
test/mp_invoke.cpp
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@@ -35,6 +35,11 @@ struct Q4
template<class T1, class... T> using fn = T1; template<class T1, class... T> using fn = T1;
}; };
struct Q5
{
template<class T1, class T2> using fn = T2;
};
int main() int main()
{ {
BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q1>, void>)); BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q1>, void>));
@@ -52,5 +57,7 @@ int main()
BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q4, int>, int>)); BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q4, int>, int>));
BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q4, int[], char[]>, int[]>)); BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q4, int[], char[]>, int[]>));
BOOST_TEST_TRAIT_TRUE((std::is_same<mp_invoke<Q5, int, float>, float>));
return boost::report_errors(); return boost::report_errors();
} }

11
test/mp_quote.cpp
View File

@@ -24,7 +24,7 @@ struct D1: B {};
struct D2: B {}; struct D2: B {};
struct ND {}; struct ND {};
template<class... T> using is_base_of_t = typename std::is_base_of<T...>::type; template<class T, class U> using is_base_of_t = typename std::is_base_of<T, U>::type;
int main() int main()
{ {
@@ -54,10 +54,11 @@ int main()
{ {
using Q = mp_quote<mp_identity_t>; using Q = mp_quote<mp_identity_t>;
// using R1 = Y<Q::fn, void, char, int>; #if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
// BOOST_TEST_TRAIT_TRUE((std::is_same<R1, X<void, char, int>>)); #else
// using R1 = Y<Q::fn, void, char, int>;
// error: pack expansion used as argument for non-pack parameter of alias template BOOST_TEST_TRAIT_TRUE((std::is_same<R1, X<void, char, int>>));
#endif
#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, <= 1910 && BOOST_MSVC >= 1900 ) #if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, <= 1910 && BOOST_MSVC >= 1900 )
#else #else