From a7873e975d67b69308976e695f25c6d97ec52238 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ion=20Gazta=C3=B1aga?= <igaztanaga@gmail.com>
Date: Sat, 1 Nov 2025 11:49:49 +0100
Subject: [PATCH] Add erase_if for set/flat_set

---
 include/boost/container/detail/algorithm.hpp | 22 +++++++++
 include/boost/container/flat_set.hpp         | 19 ++++++++
 include/boost/container/set.hpp              | 19 ++++++++
 test/set_test.hpp                            | 49 ++++++++++++++++++++
 4 files changed, 109 insertions(+)

diff --git a/include/boost/container/detail/algorithm.hpp b/include/boost/container/detail/algorithm.hpp
index 38399d8..93ad74d 100644
--- a/include/boost/container/detail/algorithm.hpp
+++ b/include/boost/container/detail/algorithm.hpp
@@ -213,6 +213,28 @@ FwdIt remove_if(FwdIt first, FwdIt last, Pred p)
     return first;
 }
 
+template <class Cont, class Pred>
+typename Cont::size_type container_erase_if(Cont& c, Pred p)
+{
+   typedef typename Cont::size_type size_type;
+   typedef typename Cont::iterator  it_t;
+
+   size_type prev_size = c.size();
+   it_t it         = c.begin();
+
+   //end() must be called each loop for non-node containers
+   while ( it != c.end() ) {
+      if (p(*it)) {
+         it = c.erase(it);
+      }
+      else {
+         ++it;
+      }
+   }
+
+   return prev_size - c.size();
+}
+
 }  //namespace container {
 }  //namespace boost {
 
diff --git a/include/boost/container/flat_set.hpp b/include/boost/container/flat_set.hpp
index caffd16..7ee5ada 100644
--- a/include/boost/container/flat_set.hpp
+++ b/include/boost/container/flat_set.hpp
@@ -28,6 +28,7 @@
 // container/detail
 #include <boost/container/detail/flat_tree.hpp>
 #include <boost/container/detail/mpl.hpp>
+#include <boost/container/detail/algorithm.hpp>
 // move
 #include <boost/move/traits.hpp>
 #include <boost/move/utility_core.hpp>
@@ -1132,6 +1133,15 @@ class flat_set
    {  return this->get_sequence_cref();  }
 };
 
+//! <b>Effects</b>: Erases all elements that satisfy the predicate pred from the container c.
+//!
+//! <b>Complexity</b>: Linear.
+template <class K, class C, class A, class Pred>
+inline typename flat_set<K, C, A>::size_type erase_if(flat_set<K, C, A>& c, Pred pred)
+{
+   return container_erase_if(c, pred);
+}
+
 #ifndef BOOST_CONTAINER_NO_CXX17_CTAD
 
 template <typename InputIterator>
@@ -1863,6 +1873,15 @@ class flat_multiset
    {  return this->get_sequence_cref();  }
 };
 
+//! <b>Effects</b>: Erases all elements that satisfy the predicate pred from the container c.
+//!
+//! <b>Complexity</b>: Linear.
+template <class K, class C, class A, class Pred>
+inline typename flat_multiset<K, C, A>::size_type erase_if(flat_multiset<K, C, A>& c, Pred pred)
+{
+   return container_erase_if(c, pred);
+}
+
 #ifndef BOOST_CONTAINER_NO_CXX17_CTAD
 
 template <typename InputIterator>
diff --git a/include/boost/container/set.hpp b/include/boost/container/set.hpp
index e71a1ec..4974f72 100644
--- a/include/boost/container/set.hpp
+++ b/include/boost/container/set.hpp
@@ -27,6 +27,7 @@
 #include <boost/container/detail/mpl.hpp>
 #include <boost/container/detail/tree.hpp>
 #include <boost/container/new_allocator.hpp> //new_allocator
+#include <boost/container/detail/algorithm.hpp>
 // intrusive/detail
 #include <boost/intrusive/detail/minimal_pair_header.hpp>      //pair
 #include <boost/intrusive/detail/minimal_less_equal_header.hpp>//less, equal
@@ -957,6 +958,15 @@ class set
    #endif   //#if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
 };
 
+//! <b>Effects</b>: Erases all elements that satisfy the predicate pred from the container c.
+//!
+//! <b>Complexity</b>: Linear.
+template <class K, class C, class A, class O, class Pred>
+inline typename set<K, C, A, O>::size_type erase_if(set<K, C, A, O>& c, Pred pred)
+{
+   return container_erase_if(c, pred);
+}
+
 #ifndef BOOST_CONTAINER_NO_CXX17_CTAD
 
 template <typename InputIterator>
@@ -1612,6 +1622,15 @@ class multiset
    #endif   //#if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
 };
 
+//! <b>Effects</b>: Erases all elements that satisfy the predicate pred from the container c.
+//!
+//! <b>Complexity</b>: Linear.
+template <class K, class C, class A, class O, class Pred>
+inline typename multiset<K, C, A, O>::size_type erase_if(multiset<K, C, A, O>& c, Pred pred)
+{
+   return container_erase_if(c, pred);
+}
+
 #ifndef BOOST_CONTAINER_NO_CXX17_CTAD
 
 template <typename InputIterator>
diff --git a/test/set_test.hpp b/test/set_test.hpp
index 5846748..b564424 100644
--- a/test/set_test.hpp
+++ b/test/set_test.hpp
@@ -12,6 +12,7 @@
 #define BOOST_CONTAINER_TEST_SET_TEST_HEADER
 
 #include <boost/container/detail/config_begin.hpp>
+#include <boost/container/detail/compare_functors.hpp>
 #include "check_equal_containers.hpp"
 #include "print_container.hpp"
 #include "movable_int.hpp"
@@ -823,6 +824,54 @@ int set_test ()
       if(!CheckEqualContainers(boostmultiset, stdmultiset)) return 1;
    }
 
+   {  //erase_if
+      boostset.clear();
+      boostmultiset.clear();
+      stdset.clear();
+      stdmultiset.clear();
+
+      {
+         IntType aux_vect[(std::size_t)MaxElem];
+         IntType aux_vect2[(std::size_t)MaxElem];
+         IntType aux_vect3[(std::size_t)MaxElem];
+
+         for(int i = 0; i < MaxElem; ++i){
+            aux_vect[i] = i;
+            aux_vect2[i] = i;
+            aux_vect3[i] = i;
+         }
+
+         boostset.     insert(boost::make_move_iterator(&aux_vect[0]),  boost::make_move_iterator(&aux_vect[0]  + MaxElem));
+         boostmultiset.insert(boost::make_move_iterator(&aux_vect2[0]), boost::make_move_iterator(&aux_vect2[0] + MaxElem));
+         boostmultiset.insert(boost::make_move_iterator(&aux_vect3[0]), boost::make_move_iterator(&aux_vect3[0] + MaxElem));
+      }
+
+      for(int i = 0; i < MaxElem; ++i){
+         stdset.insert(i);
+         stdmultiset.insert(i);
+         stdmultiset.insert(i);
+      }
+
+      for(int i = 0; i < MaxElem; ++i) {
+         //erase_if
+         const int setkey = (i + MaxElem/2) % MaxElem;
+         if (1 != erase_if(boostset, equal_to_value<int>(setkey)))
+            return 1;
+         if (0 != erase_if(boostset, equal_to_value<int>(setkey)))
+            return 1;
+         stdset.erase(setkey);
+         if(!test::CheckEqualContainers(boostset, stdset)) return false;
+
+         //erase_if
+         if (2 != erase_if(boostmultiset, equal_to_value<int>(setkey)))
+            return 1;
+         if (0 != erase_if(boostmultiset, equal_to_value<int>(setkey)))
+            return 1;
+         stdmultiset.erase(setkey);
+         if(!test::CheckEqualContainers(boostmultiset, stdmultiset)) return false;
+      }
+   }
+
    if(set_test_copyable<MyBoostSet, MyStdSet, MyBoostMultiSet, MyStdMultiSet>
       (dtl::bool_<boost::container::test::is_copyable<IntType>::value>())){
       return 1;