From 20aa1aee7e34c49839b58560f338efbd557c9f31 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ion=20Gazta=C3=B1aga?= <igaztanaga@gmail.com>
Date: Thu, 22 Jan 2026 00:09:11 +0100
Subject: [PATCH] Implement "ends_with" and update "starts_with" to the same
 implementation style.

---
 doc/container.qbk                  |  2 +-
 include/boost/container/string.hpp | 46 ++++++++++++++++++++++++++++--
 test/string_test.cpp               | 32 ++++++---------------
 3 files changed, 52 insertions(+), 28 deletions(-)

diff --git a/doc/container.qbk b/doc/container.qbk
index f1664ee..336b6b9 100644
--- a/doc/container.qbk
+++ b/doc/container.qbk
@@ -1461,7 +1461,7 @@ use [*Boost.Container]? There are several reasons for that:
 * 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.
-   * Added C++20 `starts_with` and C++23 `contains` overloads.
+   * Added C++20 `starts_with`/`ends_with` and 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 fc88a54..2265cd2 100644
--- a/include/boost/container/string.hpp
+++ b/include/boost/container/string.hpp
@@ -2989,7 +2989,11 @@ class basic_string
    template<template <class, class> class BasicStringView>
    BOOST_CONTAINER_NODISCARD inline
       bool starts_with(BasicStringView<CharT, Traits> sv) const BOOST_NOEXCEPT
-   {  return this->size() >= sv.size() && Traits::compare(this->data(), sv.data(), sv.size()) == 0;  }
+   {
+      const std::size_t s_sz = sv.size();
+      const std::size_t t_sz = this->size();
+      return t_sz >= s_sz && Traits::compare(this->data(), sv.data(), s_sz) == 0;
+   }
 
    //! <b>Effects</b>: Checks if the string begins with the given prefix
    //!
@@ -3008,11 +3012,47 @@ class basic_string
    BOOST_CONTAINER_NODISCARD inline
       bool starts_with(const CharT* s) const BOOST_NOEXCEPT
    {
-      const size_type s_sz = Traits::length(s);
-      const size_type t_sz = this->size();
+      const std::size_t s_sz = Traits::length(s);
+      const std::size_t t_sz = this->size();
       return t_sz >= s_sz && Traits::compare(this->data(), s, s_sz) == 0;
    }
 
+   //! <b>Effects</b>: Checks if the string begins with the given suffix
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string begins with the provided suffix, false otherwise.
+   template<template <class, class> class BasicStringView>
+   BOOST_CONTAINER_NODISCARD inline
+      bool ends_with(BasicStringView<CharT, Traits> sv) const BOOST_NOEXCEPT
+   {
+      const std::size_t s_sz = sv.size();
+      const std::size_t t_sz = this->size();
+      return t_sz >= s_sz && Traits::compare(this->data() + std::ptrdiff_t(t_sz - s_sz), sv.data(), s_sz) == 0;
+   }
+
+   //! <b>Effects</b>: Checks if the string begins with the given suffix
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string begins with the provided suffix, false otherwise.
+   BOOST_CONTAINER_NODISCARD inline
+      bool ends_with(CharT c) const BOOST_NOEXCEPT
+   {  return !empty() && Traits::eq(back(), c);  }
+
+   //! <b>Effects</b>: Checks if the string begins with the given suffix
+   //!
+   //! <b>Throws</b>: Nothing
+   //!
+   //! <b>Returns</b>: true if the string begins with the provided suffix, false otherwise.
+   BOOST_CONTAINER_NODISCARD inline
+      bool ends_with(const CharT* s) const BOOST_NOEXCEPT
+   {
+      const std::size_t s_sz = Traits::length(s);
+      const std::size_t t_sz = this->size();
+      return t_sz >= s_sz && Traits::compare(this->data() + std::ptrdiff_t(t_sz - s_sz), s, s_sz) == 0;
+   }
+
    #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 167ed7d..1030e66 100644
--- a/test/string_test.cpp
+++ b/test/string_test.cpp
@@ -1473,24 +1473,9 @@ void test_compare()
 }
 
 //==============================================================================
-// SECTION 11: Operations - starts_with, ends_with, contains (helper functions)
-// Note: boost::container::string may not have these methods, so we implement
-// them using find/compare for testing purposes
+// SECTION 11: Operations - starts_with, ends_with, contains
 //==============================================================================
 
-// Helper functions for starts_with/ends_with/contains since boost::container::string
-// might not have these methods in older versions
-namespace test_helpers {
-
-   bool ends_with(const string& s, const char* suffix) {
-      string::size_type len = std::strlen(suffix);
-      return s.size() >= len && s.compare(s.size() - len, len, suffix) == 0;
-   }
-   bool ends_with(const string& s, char c) {
-      return !s.empty() && s[s.size() - 1] == c;
-   }
-}
-
 void test_starts_with()
 {
    string s("Hello, World!");
@@ -1509,15 +1494,14 @@ void test_ends_with()
 {
    string s("Hello, World!");
 
-   using test_helpers::ends_with;
-   BOOST_TEST(ends_with(s, "World!"));
-   BOOST_TEST(ends_with(s, "!"));
-   BOOST_TEST(ends_with(s, ""));
-   BOOST_TEST(ends_with(s, '!'));
+   BOOST_TEST(s.ends_with("World!"));
+   BOOST_TEST(s.ends_with("!"));
+   BOOST_TEST(s.ends_with(""));
+   BOOST_TEST(s.ends_with('!'));
 
-   BOOST_TEST(!ends_with(s, "Hello"));
-   BOOST_TEST(!ends_with(s, "world!")); // case-sensitive
-   BOOST_TEST(!ends_with(s, 'H'));
+   BOOST_TEST(!s.ends_with("Hello"));
+   BOOST_TEST(!s.ends_with("world!")); // case-sensitive
+   BOOST_TEST(!s.ends_with('H'));
 }
 
 void test_contains()