Add mp_valid, mp_defer, mp_defer_if_valid.

include/boost/mp11/utility.hpp

@@ -8,6 +8,8 @@
 //  See accompanying file LICENSE_1_0.txt or copy at
 //  http://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/mp11/integral.hpp>
+
 namespace boost
 {
 
@@ -63,8 +65,30 @@ template<bool C, class T, template<class...> class F, class... U> using mp_eval_
 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
+{
+
+template<template<class...> class F, class... T> struct mp_valid_impl
+{
+    template<template<class...> class G, class = G<T...>> static mp_true check(int);
+    template<template<class...> class> static mp_false check(...);
+
+    using type = decltype(check<F>(0));
+};
+
+} // namespace detail
+
+template<template<class...> class F, class... T> using mp_valid = typename detail::mp_valid_impl<F, T...>::type;
+
 // mp_defer
+template<template<class...> class F, class... T> struct mp_defer
+{
+    using type = F<T...>;
+};
+
 // mp_defer_if_valid
+template<template<class...> class F, class... T> using mp_defer_if_valid = mp_if<mp_valid<F, T...>, mp_defer<F, T...>, mp_inherit<>>;
 
 } // namespace boost
 

test/Jamfile.v2

@@ -57,6 +57,9 @@ run mp_identity.cpp : : : $(REQ) ;
 run mp_inherit.cpp : : : $(REQ) ;
 run mp_if.cpp : : : $(REQ) ;
 run mp_eval_if.cpp : : : $(REQ) ;
+run mp_valid.cpp : : : $(REQ) ;
+run mp_defer.cpp : : : $(REQ) ;
+run mp_defer_if_valid.cpp : : : $(REQ) ;
 
 # integer_sequence
 run integer_sequence.cpp : : : $(REQ) ;

test/mp_defer.cpp

@@ -0,0 +1,26 @@
+
+//  Copyright 2015 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>
+
+template<class T> using add_pointer = T*;
+
+using boost::mp_defer;
+
+template<class T> using add_pointer_impl = mp_defer<add_pointer, T>;
+
+int main()
+{
+    BOOST_TEST_TRAIT_TRUE((std::is_same<add_pointer_impl<void>::type, void*>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<add_pointer_impl<int>::type, int*>));
+
+    return boost::report_errors();
+}

test/mp_defer_if_valid.cpp

@@ -0,0 +1,29 @@
+
+//  Copyright 2015 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::mp_defer_if_valid;
+using boost::mp_identity;
+
+template<class... T> using mp_identity_2 = typename mp_defer_if_valid<mp_identity, T...>::type;
+
+int main()
+{
+    using boost::mp_valid;
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_identity_2>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_identity_2, void>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_identity_2<void>, mp_identity<void>>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_identity_2, void, void>));
+
+    return boost::report_errors();
+}

test/mp_valid.cpp

@@ -0,0 +1,72 @@
+
+//  Copyright 2015 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>
+
+template<class T> struct Xi
+{
+};
+
+template<> struct Xi<void>
+{
+    using type = void;
+};
+
+template<class T> using X = typename Xi<T>::type;
+
+template<class T> using add_pointer = T*;
+template<class T> using add_reference = T&;
+template<class T> using add_extents = T[];
+
+int main()
+{
+    using boost::mp_valid;
+    using boost::mp_identity;
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_identity>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_identity, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_identity, void, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<X>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<X, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<X, int>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<X, void, void>));
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_pointer>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<add_pointer, void>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<add_pointer, int>));
+#if !defined( BOOST_MSVC ) || !BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
+    // msvc-12.0 can form pointer to reference
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_pointer, int&>));
+#endif
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_pointer, void, void>));
+
+#if !defined( BOOST_GCC ) || !BOOST_WORKAROUND( BOOST_GCC, <= 40902 )
+    // g++ 4.9.2 doesn't like add_reference for some reason or other
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_reference>));
+#if !defined( BOOST_MSVC ) || !BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
+    // msvc-12.0 gives an internal error here
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_reference, void>));
+#endif
+    BOOST_TEST_TRAIT_TRUE((mp_valid<add_reference, int>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_reference, int, int>));
+#endif
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_extents>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<add_extents, int>));
+#if !defined( BOOST_MSVC ) || !BOOST_WORKAROUND( BOOST_MSVC, <= 1800 )
+    // msvc-12.0 can form arrays to void or int&
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_extents, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_extents, int&>));
+#endif
+    BOOST_TEST_TRAIT_FALSE((mp_valid<add_extents, int, int>));
+
+    return boost::report_errors();
+}