libcxx/test/std/utilities/meta/meta.rel/is_invocable_r.compile.pass.cpp

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // UNSUPPORTED: c++03, c++11, c++14
  10
  11 // is_invocable_r
  12
  13 #include <type_traits>
  14
  15 // Non-invocable types
  16
  17 static_assert(!std::is_invocable_r<void, void>::value);
  18 static_assert(!std::is_invocable_r<void, int>::value);
  19 static_assert(!std::is_invocable_r<void, int*>::value);
  20 static_assert(!std::is_invocable_r<void, int&>::value);
  21 static_assert(!std::is_invocable_r<void, int&&>::value);
  22
  23 // Result type matches
  24
  25 template <typename T>
  26 T Return();
  27
  28 static_assert(std::is_invocable_r<int, decltype(Return<int>)>::value);
  29 static_assert(std::is_invocable_r<char, decltype(Return<char>)>::value);
  30 static_assert(std::is_invocable_r<int*, decltype(Return<int*>)>::value);
  31 static_assert(std::is_invocable_r<int&, decltype(Return<int&>)>::value);
  32 static_assert(std::is_invocable_r<int&&, decltype(Return<int&&>)>::value);
  33
  34 // void result type
  35
  36 // Any actual return type should be useable with a result type of void.
  37 static_assert(std::is_invocable_r<void, decltype(Return<void>)>::value);
  38 static_assert(std::is_invocable_r<void, decltype(Return<int>)>::value);
  39 static_assert(std::is_invocable_r<void, decltype(Return<int*>)>::value);
  40 static_assert(std::is_invocable_r<void, decltype(Return<int&>)>::value);
  41 static_assert(std::is_invocable_r<void, decltype(Return<int&&>)>::value);
  42
  43 // const- and volatile-qualified void should work too.
  44 static_assert(std::is_invocable_r<const void, decltype(Return<void>)>::value);
  45 static_assert(std::is_invocable_r<const void, decltype(Return<int>)>::value);
  46 static_assert(std::is_invocable_r<volatile void, decltype(Return<void>)>::value);
  47 static_assert(std::is_invocable_r<volatile void, decltype(Return<int>)>::value);
  48 static_assert(std::is_invocable_r<const volatile void, decltype(Return<void>)>::value);
  49 static_assert(std::is_invocable_r<const volatile void, decltype(Return<int>)>::value);
  50
  51 // Conversion of result type
  52
  53 // It should be possible to use a result type to which the actual return type
  54 // can be converted.
  55 static_assert(std::is_invocable_r<char, decltype(Return<int>)>::value);
  56 static_assert(std::is_invocable_r<const int*, decltype(Return<int*>)>::value);
  57 static_assert(std::is_invocable_r<void*, decltype(Return<int*>)>::value);
  58 static_assert(std::is_invocable_r<const int&, decltype(Return<int>)>::value);
  59 static_assert(std::is_invocable_r<const int&, decltype(Return<int&>)>::value);
  60 static_assert(std::is_invocable_r<const int&, decltype(Return<int&&>)>::value);
  61 static_assert(std::is_invocable_r<const char&, decltype(Return<int>)>::value);
  62
  63 // But not a result type where the conversion doesn't work.
  64 static_assert(!std::is_invocable_r<int, decltype(Return<void>)>::value);
  65 static_assert(!std::is_invocable_r<int, decltype(Return<int*>)>::value);
  66
  67 // Non-moveable result type
  68
  69 // Define a type that can't be move-constructed.
  70 struct CantMove {
  71   CantMove() = default;
  72   CantMove(CantMove&&) = delete;
  73 };
  74
  75 static_assert(!std::is_move_constructible_v<CantMove>);
  76 static_assert(!std::is_copy_constructible_v<CantMove>);
  77
  78 // Define functions that return that type.
  79 CantMove MakeCantMove() { return {}; }
  80 CantMove MakeCantMoveWithArg(int) { return {}; }
  81
  82 // Assumption check: it should be possible to call one of those functions and
  83 // use it to initialize a CantMove object.
  84 CantMove cant_move = MakeCantMove();
  85
  86 // Therefore std::is_invocable_r should agree that they can be invoked to yield
  87 // a CantMove.
  88 static_assert(std::is_invocable_r<CantMove, decltype(MakeCantMove)>::value);
  89 static_assert(std::is_invocable_r<CantMove, decltype(MakeCantMoveWithArg), int>::value);
  90
  91 // Of course it still shouldn't be possible to call one of the functions and get
  92 // back some other type.
  93 static_assert(!std::is_invocable_r<int, decltype(MakeCantMove)>::value);
  94
  95 // And the argument types should still be important.
  96 static_assert(!std::is_invocable_r<CantMove, decltype(MakeCantMove), int>::value);
  97 static_assert(!std::is_invocable_r<CantMove, decltype(MakeCantMoveWithArg)>::value);
  98
  99 // is_invocable_r
 100
 101 // The struct form should be available too, not just the _v variant.
 102 static_assert(std::is_invocable_r<int, decltype(Return<int>)>::value);
 103 static_assert(!std::is_invocable_r<int*, decltype(Return<int>)>::value);