libcxx/test/std/strings/basic.string/string.cons/from_range_deduction.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 // <string>
  10
  11 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
  12 // To silence a GCC warning-turned-error re. `BadAlloc::value_type`.
  13 // ADDITIONAL_COMPILE_FLAGS: -Wno-unused-local-typedefs
  14
  15 // template<ranges::input_range R,
  16 //          class Allocator = allocator<ranges::range_value_t<R>>>
  17 //   basic_string(from_range_t, R&&, Allocator = Allocator())
  18 //     -> basic_string<ranges::range_value_t<R>, char_traits<ranges::range_value_t<R>>,
  19 //                     Allocator>; // C++23
  20 //
  21 // The deduction guide shall not participate in overload resolution if Allocator
  22 // is a type that does not qualify as an allocator (in addition to the `input_range` concept being satisfied by `R`).
  23
  24 #include <array>
  25 #include <string>
  26
  27 #include "deduction_guides_sfinae_checks.h"
  28 #include "test_allocator.h"
  29
  30 int main(int, char**) {
  31   using Char = char16_t;
  32
  33   {
  34     std::basic_string c(std::from_range, std::array<Char, 0>());
  35     static_assert(std::is_same_v<decltype(c), std::basic_string<Char>>);
  36   }
  37
  38   {
  39     using Alloc = test_allocator<Char>;
  40     std::basic_string c(std::from_range, std::array<Char, 0>(), Alloc());
  41     static_assert(std::is_same_v<decltype(c), std::basic_string<Char, std::char_traits<Char>, Alloc>>);
  42   }
  43
  44   // Note: defining `value_type` is a workaround because one of the deduction guides will end up instantiating
  45   // `basic_string`, and that would fail with a hard error if the given allocator doesn't define `value_type`.
  46   struct BadAlloc {
  47     using value_type = char;
  48   };
  49   SequenceContainerDeductionGuidesSfinaeAway<std::basic_string, std::basic_string<char>, BadAlloc>();
  50
  51   return 0;
  52 }