[libcxx-commits] [libcxx] [libc++][string] P3044R2: sub-`string_view` from `string` (PR #147095)

[Hristo Hristov via libcxx-commits]

================
@@ -0,0 +1,127 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+
+// <string_view>
+
+// constexpr basic_string_view subview(size_type pos = 0,
+//                                     size_type n = npos) const;      // freestanding-deleted
+
+#include <cassert>
+#include <concepts>
+#include <string_view>
+#include <utility>
+
+#include "constexpr_char_traits.h"
+#include "make_string.h"
+#include "test_macros.h"
+
+#define CS(S) MAKE_CSTRING(CharT, S)
+
+template <typename CharT, typename TraitsT>
+constexpr void test() {
+  std::basic_string_view<CharT, TraitsT> sv{CS("Hello cruel world!")};
+
+  { // With a default position and a character length.
+
+    // Check if subview() is a const-qualified.
+    assert(std::as_const(sv).subview() == CS("Hello cruel world!"));
+
+    // Check if the return type of subview() is correct.
+    std::same_as<std::basic_string_view<CharT, TraitsT>> decltype(auto) subsv = sv.subview();
+    assert(subsv == CS("Hello cruel world!"));
+  }
+
+  { // Check with different position and length.
+
+    // With a explict position and a character length.
+    assert(sv.subview(6, 5) == CS("cruel"));
+
+    // From the beginning of the string with a explicit character length.
+    assert(sv.subview(0, 5) == CS("Hello"));
+
+    // To the end of string with the default character length.
+    assert(sv.subview(12) == CS("world!"));
+
+    // From the beginning to the end of the string with explicit values.
+    assert(sv.subview(0, sv.size()) == CS("Hello cruel world!"));
+  }
+
+  // Test if exceptions are thrown correctly.
+#ifndef TEST_HAS_NO_EXCEPTIONS
+  if (!std::is_constant_evaluated()) {
+    { // With a position that is out of range.
+      try {
+        sv.subview(sv.size() + 1);
+        assert(false && "Expected std::out_of_range exception");
+      } catch ([[maybe_unused]] const std::out_of_range& ex) {
+        LIBCPP_ASSERT(std::string(ex.what()) == "string_view::subview");
+      } catch (...) {
+        assert(false && "Expected std::out_of_range exception");
+      }
+    }
+
+    { // With a position that is out of range and a 0 character length.
+      try {
+        sv.subview(sv.size() + 1, 0);
+        assert(false && "Expected std::out_of_range exception");
+      } catch ([[maybe_unused]] const std::out_of_range& ex) {
+        LIBCPP_ASSERT(std::string(ex.what()) == "string_view::subview");
+      } catch (...) {
+        assert(false && "Expected std::out_of_range exception");
+      }
+    }
+
+    { // With a position that is out of range and a some character length.
+      try {
+        sv.subview(sv.size() + 1, 1);
+        assert(false && "Expected std::out_of_range exception");
+      } catch ([[maybe_unused]] const std::out_of_range& ex) {
+        LIBCPP_ASSERT(std::string(ex.what()) == "string_view::subview");
+      } catch (...) {
+        assert(false && "Expected std::out_of_range exception");
+      }
+    }
+  }
+#endif
+}
+
+template <typename CharT>
+constexpr void test() {
+  test<CharT, std::char_traits<CharT>>();
+  test<CharT, std::char_traits<CharT>>();
+  test<CharT, std::char_traits<CharT>>();
+  test<CharT, std::char_traits<CharT>>();
+
+  test<CharT, constexpr_char_traits<CharT>>();
+  test<CharT, constexpr_char_traits<CharT>>();
+  test<CharT, constexpr_char_traits<CharT>>();
+  test<CharT, constexpr_char_traits<CharT>>();
+}
+
+constexpr bool test() {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+#ifndef TEST_HAS_NO_CHAR8_T
+  test<char8_t>();
+#endif
+  test<char16_t>();
+  test<char32_t>();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  // static_assert(test());
----------------
H-G-Hristov wrote:

```suggestion
  static_assert(test());
```

https://github.com/llvm/llvm-project/pull/147095