diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -985,6 +985,17 @@
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 void resize(size_type __n) {resize(__n, value_type());}
 
     _LIBCPP_CONSTEXPR_AFTER_CXX17 void reserve(size_type __requested_capacity);
+
+#if _LIBCPP_STD_VER > 20
+    template <class _Operation>
+    _LIBCPP_HIDE_FROM_ABI constexpr void resize_and_overwrite(size_type __n, _Operation __op)
+        requires requires(_Operation __o) { {__o(pointer{}, size_type{})} -> _VSTD::convertible_to<size_type>; } {
+      if (__n > capacity())
+          __shrink_or_extend(__recommend(__n));
+      __erase_to_end(__op(data(), __n));
+    }
+#endif
+
     _LIBCPP_INLINE_VISIBILITY void __resize_default_init(size_type __n);
 
     _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_INLINE_VISIBILITY void reserve() _NOEXCEPT {shrink_to_fit();}
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp
@@ -0,0 +1,79 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <string>
+
+// void resize_and_overwrite(size_type n, Operation op)
+
+#include <cassert>
+#include <string>
+
+template <class S>
+constexpr void test_exact_size(S s) {
+  S s2;
+  s2.resize_and_overwrite(s.size() * 2, [&](char* begin, size_t size) {
+    assert(size == s.size() * 2);
+    std::copy(s.begin(), s.end(), begin);
+    std::copy(s.begin(), s.end(), begin + s.size());
+    return s.size() * 2;
+  });
+  assert(s2 == s + s);
+}
+
+template <class S>
+constexpr void test_oversized(S s) {
+  S s2;
+  s2.resize_and_overwrite(s.size() * 3, [&](char* begin, size_t size) {
+    assert(size == s.size() * 3);
+    std::copy(s.begin(), s.end(), begin);
+    std::copy(s.begin(), s.end(), begin + s.size());
+    return s.size() * 2;
+  });
+  assert(s2.size() == s.size() * 2);
+  assert(s2.capacity() >= s.size() * 3);
+  assert(s2 == s + s);
+}
+
+template <class S>
+constexpr void test_undersized(S s) {
+  S s2;
+  s2.resize_and_overwrite(s.size() + s.size() / 2, [&](char* begin, size_t size) {
+    assert(size == s.size() + s.size() / 2);
+    std::copy(s.begin(), s.end(), begin);
+    std::copy(s.begin(), s.begin() + s.size() / 2, begin + s.size());
+    return size;
+  });
+  assert(s2 == s + s.substr(0, s.size() / 2));
+}
+
+template <class S>
+constexpr void test_all(S s) {
+  test_exact_size(s);
+  test_oversized(s);
+  test_undersized(s);
+}
+
+constexpr bool test() {
+  using S = std::string;
+  test_all<S>("");
+  test_all<S>("Banane");
+  test_all<S>("a+sgpion");
+  test_all<S>("dafgiudpfm12");
+  test_all<S>("adfpoguharsüoginasfdü23");
+  test_all<S>("asoriübsfogiabsdfgoüif24");
+  test_all<S>("long long string so no SSO");
+  test_all<S>("pioegarsipasngipnadfgipkonadfpioknadfgöpaionge48");
+  return true;
+}
+
+int main() {
+  test();
+  static_assert(test());
+}