P1391R4 "Range Constructor for string_view" (#1245)

stl/inc/xstring

@@ -1240,6 +1240,15 @@ public:
 #endif // _CONTAINER_DEBUG_LEVEL > 0
     }
 
+#ifdef __cpp_lib_concepts
+    // clang-format off
+    template <contiguous_iterator _It, sized_sentinel_for<_It> _Se>
+        requires (is_same_v<iter_value_t<_It>, _Elem> && !is_convertible_v<_Se, size_type>)
+    constexpr basic_string_view(_It _First, _Se _Last) noexcept // strengthened
+        : _Mydata(_STD to_address(_First)), _Mysize(static_cast<size_type>(_Last - _First)) {}
+    // clang-format on
+#endif // __cpp_lib_concepts
+
     _NODISCARD constexpr const_iterator begin() const noexcept {
 #if _ITERATOR_DEBUG_LEVEL >= 1
         return const_iterator(_Mydata, _Mysize, 0);
@@ -1628,6 +1637,9 @@ private:
 };
 
 #ifdef __cpp_lib_concepts
+template <contiguous_iterator _It, sized_sentinel_for<_It> _Se>
+basic_string_view(_It, _Se) -> basic_string_view<iter_value_t<_It>>;
+
 namespace ranges {
     template <class _Elem, class _Traits>
     inline constexpr bool enable_view<basic_string_view<_Elem, _Traits>> = true;

tests/std/tests/P0220R1_string_view/test.cpp

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <array>
 #include <assert.h>
 #include <sstream>
 #include <stdexcept>
@@ -303,6 +304,24 @@ constexpr bool test_case_buffer_constructor() {
     return true;
 }
 
+constexpr bool test_case_contiguous_constructor() {
+#ifdef __cpp_lib_concepts
+    const array expectedData{'n', 'o', ' ', 'n', 'u', 'l', 'l'};
+    // Also tests the corresponding deduction guide:
+    same_as<string_view> auto sv = basic_string_view(expectedData.begin(), expectedData.end());
+    assert(sv.data() == expectedData.data());
+    assert(sv.size() == 7);
+    assert(sv.length() == 7);
+    assert(!sv.empty());
+    assert(sv[1] == 'o');
+    assert(sv.at(1) == 'o');
+    assert(sv.front() == 'n');
+    assert(sv.back() == 'l');
+#endif // __cpp_lib_concepts
+
+    return true;
+}
+
 template <class CharT, class Traits>
 constexpr bool test_case_iterators() {
     using iterator = typename basic_string_view<CharT, Traits>::iterator;
@@ -1028,6 +1047,7 @@ static_assert(c_string_view{"abcd"} == "abcd");
 static_assert(test_case_default_constructor());
 static_assert(test_case_ntcts_constructor<constexpr_char_traits>());
 static_assert(test_case_buffer_constructor());
+static_assert(test_case_contiguous_constructor());
 #if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-284079 "C1XX's C++14 constexpr emits bogus warnings C4146,
                                            // C4308, C4307 for basic_string_view::iterator"
 static_assert(test_case_iterators<char, constexpr_char_traits>());
@@ -1072,6 +1092,7 @@ int main() {
     test_case_default_constructor();
     test_case_ntcts_constructor();
     test_case_buffer_constructor();
+    test_case_contiguous_constructor();
     test_case_iterators<char, char_traits<char>>();
     test_case_iterators<wchar_t, char_traits<wchar_t>>();
     test_case_prefix<char, char_traits<char>>();