From a02aae0b9fdedf54d8ceacf758fe53a3f081df96 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ion=20Gazta=C3=B1aga?= <igaztanaga@gmail.com>
Date: Wed, 21 Jan 2026 22:46:19 +0100
Subject: [PATCH] Add C++23 "contains" to basic_string.

---
 doc/container.qbk                  |  4 +++-
 include/boost/container/string.hpp | 28 ++++++++++++++++++++++++++++
 test/string_test.cpp               | 17 ++++++++---------
 3 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/doc/container.qbk b/doc/container.qbk
index 7d0a249..51ac0c1 100644
--- a/doc/container.qbk
+++ b/doc/container.qbk
@@ -1459,7 +1459,9 @@ use [*Boost.Container]? There are several reasons for that:
    * If available, uses C++17's utilities under the `__cpp_aligned_new` feature.
    * Uses alternative aligned allocation functions (`posix_memalign`, `aligned_alloc`, `_aligned_malloc`...) otherwise.
 * Implemented overaligned allocation support for `adaptive_pool`and `node_allocator`
-* Updated `basic_string` to the latest standard API: Added missing `string_view` members and updated `operator[]` to be able to return the terminating null.
+* Updated `basic_string` to the latest standard API:
+   * Added missing `string_view` members and updated `operator[]` to be able to return the terminating null.
+   * Added C++23 `contains` overloads
 * Fixed bugs/issues:
    * [@https://github.com/boostorg/container/issues/323 GitHub #323: ['"flat_tree::try_emplace UB"]].
    * [@https://github.com/boostorg/container/issues/328 GitHub #328: ['"boost::container::deque stores a redundant copy of the allocator, increasing size"]].
diff --git a/include/boost/container/string.hpp b/include/boost/container/string.hpp
index 313cc63..a8d0e89 100644
--- a/include/boost/container/string.hpp
+++ b/include/boost/container/string.hpp
@@ -2953,6 +2953,34 @@ class basic_string
       int compare(size_type pos1, size_type n1, const CharT* s) const
    {  return this->compare(pos1, n1, s, Traits::length(s)); }
 
+   //! <b>Effects</b>: Equivalent to find(sv) != npos
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string contains the provided substring, false otherwise.
+   template<template <class, class> class BasicStringView>
+   BOOST_CONTAINER_NODISCARD inline
+      bool contains(BasicStringView<CharT, Traits> sv) const BOOST_NOEXCEPT
+   {  return this->find(sv) != npos; }
+
+   //! <b>Effects</b>: Equivalent to find(c) != npos
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string contains the provided substring, false otherwise.
+   BOOST_CONTAINER_NODISCARD inline
+      bool contains(CharT c) const BOOST_NOEXCEPT
+   {  return this->find(c) != npos; }
+
+   //! <b>Effects</b>: Equivalent to find(c) != npos
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string contains the provided substring, false otherwise.
+   BOOST_CONTAINER_NODISCARD inline
+      bool contains(const CharT* s) const BOOST_NOEXCEPT
+   {  return this->find(s) != npos; }
+
    #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
    private:
    void priv_move_assign(BOOST_RV_REF(basic_string) x, dtl::bool_<true> /*steal_resources*/)
diff --git a/test/string_test.cpp b/test/string_test.cpp
index 9cd9737..ec30592 100644
--- a/test/string_test.cpp
+++ b/test/string_test.cpp
@@ -1537,16 +1537,15 @@ void test_contains()
 {
    string s("Hello, World!");
 
-   using test_helpers::contains;
-   BOOST_TEST(contains(s, "World"));
-   BOOST_TEST(contains(s, "Hello"));
-   BOOST_TEST(contains(s, ", "));
-   BOOST_TEST(contains(s, ""));
-   BOOST_TEST(contains(s, 'W'));
+   BOOST_TEST(s.contains("World"));
+   BOOST_TEST(s.contains("Hello"));
+   BOOST_TEST(s.contains(", "));
+   BOOST_TEST(s.contains(""));
+   BOOST_TEST(s.contains('W'));
 
-   BOOST_TEST(!contains(s, "world")); // case-sensitive
-   BOOST_TEST(!contains(s, "xyz"));
-   BOOST_TEST(!contains(s, 'X'));
+   BOOST_TEST(!s.contains("world")); // case-sensitive
+   BOOST_TEST(!s.contains("xyz"));
+   BOOST_TEST(!s.contains('X'));
 }
 
 //==============================================================================