Implement P1072R10 basic_string::resize_and_overwrite

stl/inc/xstring

@@ -3952,16 +3952,35 @@ public:
         );
     }
 
-    _CONSTEXPR20 void resize(_CRT_GUARDOVERFLOW const size_type _Newsize, const _Elem _Ch = _Elem()) {
+    _CONSTEXPR20 void resize(_CRT_GUARDOVERFLOW const size_type _New_size, const _Elem _Ch = _Elem()) {
         // determine new length, padding with _Ch elements as needed
         const size_type _Old_size = size();
-        if (_Newsize <= _Old_size) {
-            _Eos(_Newsize);
+        if (_New_size <= _Old_size) {
+            _Eos(_New_size);
         } else {
-            append(_Newsize - _Old_size, _Ch);
+            append(_New_size - _Old_size, _Ch);
         }
     }
 
+#if _HAS_CXX23
+    template <class _Operation>
+    constexpr void resize_and_overwrite(_CRT_GUARDOVERFLOW const size_type _New_size, _Operation _Op) {
+        if (_Mypair._Myval2._Myres < _New_size) {
+            _Reallocate_grow_by(_New_size - _Mypair._Myval2._Mysize,
+                [](_Elem* const _New_ptr, const _Elem* const _Old_ptr, const size_type _Old_size) {
+                    _Traits::copy(_New_ptr, _Old_ptr, _Old_size + 1);
+                });
+        }
+
+        const auto _Result_size = _STD move(_Op)(_Mypair._Myval2._Myptr(), _New_size);
+#if _CONTAINER_DEBUG_LEVEL > 0
+        _STL_VERIFY(_Result_size >= 0, "the returned size can't be smaller than 0");
+        _STL_VERIFY(_Result_size <= _New_size, "the returned size can't be greater than the passed size");
+#endif // _CONTAINER_DEBUG_LEVEL > 0
+        _Eos(_Result_size);
+    }
+#endif // _HAS_CXX23
+
     _NODISCARD _CONSTEXPR20 size_type capacity() const noexcept {
         return _Mypair._Myval2._Myres;
     }
@@ -4595,8 +4614,8 @@ private:
         _Mypair._Myval2._Myres = _BUF_SIZE - 1;
     }
 
-    _CONSTEXPR20 void _Eos(const size_type _Newsize) { // set new length and null terminator
-        _Traits::assign(_Mypair._Myval2._Myptr()[_Mypair._Myval2._Mysize = _Newsize], _Elem());
+    _CONSTEXPR20 void _Eos(const size_type _New_size) { // set new length and null terminator
+        _Traits::assign(_Mypair._Myval2._Myptr()[_Mypair._Myval2._Mysize = _New_size], _Elem());
     }
 
     _CONSTEXPR20 void _Tidy_init() noexcept { // initialize basic_string data members

stl/inc/yvals_core.h

@@ -276,6 +276,7 @@
 // P0448R4 <spanstream>
 // P0943R6 Supporting C Atomics In C++
 // P1048R1 is_scoped_enum
+// P1072R10 basic_string::resize_and_overwrite
 // P1132R7 out_ptr(), inout_ptr()
 // P1147R1 Printing volatile Pointers
 // P1272R4 byteswap()
@@ -1376,10 +1377,11 @@
 #define __cpp_lib_ranges_starts_ends_with 202106L
 #endif // __cpp_lib_concepts
 
-#define __cpp_lib_spanstream      202106L
-#define __cpp_lib_stdatomic_h     202011L
-#define __cpp_lib_string_contains 202011L
-#define __cpp_lib_to_underlying   202102L
+#define __cpp_lib_spanstream                  202106L
+#define __cpp_lib_stdatomic_h                 202011L
+#define __cpp_lib_string_contains             202011L
+#define __cpp_lib_string_resize_and_overwrite 202110L
+#define __cpp_lib_to_underlying               202102L
 #endif // _HAS_CXX23
 
 #define __cpp_lib_experimental_erase_if   201411L

tests/std/tests/P0980R1_constexpr_strings/test.cpp

@@ -1023,6 +1023,108 @@ constexpr bool test_interface() {
         assert(equalRanges(resized, "Helaaa"sv));
     }
 
+#if _HAS_CXX23
+    { // resize_and_overwrite
+        constexpr basic_string_view hello_fluffy_kittens = get_view_input<CharType>();
+        constexpr basic_string_view hello                = hello_fluffy_kittens.substr(0, 5);
+        constexpr basic_string_view dog                  = get_dog<CharType>();
+        constexpr basic_string_view kitten               = get_cat<CharType>();
+
+        str s;
+        s.resize_and_overwrite(5, [=](CharType* p, size_t n) {
+            assert(n == 5);
+            hello.copy(p, 5);
+            return 5u;
+        });
+
+        assert(s == hello);
+        assert(s.size() == 5);
+        assert(s.capacity() >= 5);
+        assert(s[5] == 0);
+
+        s.resize_and_overwrite(8, [=](CharType* p, size_t n) {
+            assert(n == 8);
+            assert(equal(hello.begin(), hello.end(), p, p + 5));
+            dog.copy(p, 3);
+            return 3u;
+        });
+
+        assert(s == dog);
+        assert(s.size() == 3);
+        assert(s.capacity() >= 3);
+        assert(s[3] == 0);
+
+        s.resize_and_overwrite(6, [=](CharType* p, size_t n) {
+            assert(n == 6);
+            assert(equal(dog.begin(), dog.end(), p, p + 3));
+            kitten.copy(p, 6);
+            return 6u;
+        });
+
+        assert(s == kitten);
+        assert(s.size() == 6);
+        assert(s.capacity() >= 6);
+        assert(s[6] == 0);
+
+        s.resize_and_overwrite(0, [=](CharType*, size_t n) {
+            assert(n == 0);
+            return 0u;
+        });
+
+        assert(s.size() == 0);
+        assert(s[0] == 0);
+
+        s = dog;
+
+        s.resize_and_overwrite(6, [=](CharType* p, size_t n) {
+            assert(n == 6);
+            assert(equal(dog.begin(), dog.end(), p, p + 3));
+            return 0u;
+        });
+
+        assert(s.size() == 0);
+        assert(s[0] == 0);
+
+        s = kitten;
+
+        s.resize_and_overwrite(3, [=](CharType* p, size_t n) {
+            assert(n == 3);
+            assert(equal(kitten.begin(), kitten.begin() + 3, p, p + 3));
+            dog.copy(p, 3);
+            return 3u;
+        });
+
+        assert(s == dog);
+        assert(s.size() == 3);
+        assert(s.capacity() >= 3);
+        assert(s[3] == 0);
+
+        s.resize_and_overwrite(20, [=](CharType* p, size_t n) {
+            assert(n == 20);
+            assert(equal(dog.begin(), dog.end(), p, p + 3));
+            hello_fluffy_kittens.copy(p, 20);
+            return 20u;
+        });
+
+        assert(s == hello_fluffy_kittens);
+        assert(s.size() == 20);
+        assert(s.capacity() >= 20);
+        assert(s[20] == 0);
+
+        s.resize_and_overwrite(3, [=](CharType* p, size_t n) {
+            assert(n == 3);
+            assert(equal(hello_fluffy_kittens.begin(), hello_fluffy_kittens.begin() + 3, p, p + 3));
+            dog.copy(p, 3);
+            return 3u;
+        });
+
+        assert(s == dog);
+        assert(s.size() == 3);
+        assert(s.capacity() >= 3);
+        assert(s[3] == 0);
+    }
+#endif // _HAS_CXX23
+
     { // swap
         constexpr basic_string_view<CharType> expected_first  = get_dog<CharType>();
         constexpr basic_string_view<CharType> expected_second = get_cat<CharType>();

tests/std/tests/VSO_0157762_feature_test_macros/test.compile.pass.cpp

@@ -1586,6 +1586,20 @@ STATIC_ASSERT(__cpp_lib_string_contains == 202011L);
 #endif
 #endif
 
+#if _HAS_CXX23
+#ifndef __cpp_lib_string_resize_and_overwrite
+#error __cpp_lib_string_resize_and_overwrite is not defined
+#elif __cpp_lib_string_resize_and_overwrite != 202110L
+#error __cpp_lib_string_resize_and_overwrite is not 202110L
+#else
+STATIC_ASSERT(__cpp_lib_string_resize_and_overwrite == 202110L);
+#endif
+#else
+#ifdef __cpp_lib_string_resize_and_overwrite
+#error __cpp_lib_string_resize_and_overwrite is defined
+#endif
+#endif
+
 #ifndef __cpp_lib_string_udls
 #error __cpp_lib_string_udls is not defined
 #elif __cpp_lib_string_udls != 201304L