Implement erase_if function and related tests

doc/qbk/main.qbk

@@ -32,6 +32,7 @@
 [template include_file[path][^<'''<ulink url="../../../../'''[path]'''">'''[path]'''</ulink>'''>]]
 
 [def __InputIterator__          [@https://en.cppreference.com/w/cpp/named_req/InputIterator ['InputIterator]]]
+[def __UnaryPredicate__         [@https://en.cppreference.com/w/cpp/named_req/Predicate ['Predicate]]]
 
 [/-----------------------------------------------------------------------------]
 

include/boost/static_string/static_string.hpp

@@ -5614,6 +5614,31 @@ operator+(
     std::size_t(0), +lhs);
 }
 
+//------------------------------------------------------------------------------
+//
+// erase_if
+//
+//------------------------------------------------------------------------------
+
+template<
+    std::size_t N, typename CharT,
+    typename Traits, typename UnaryPredicate>
+BOOST_STATIC_STRING_CPP14_CONSTEXPR
+typename
+basic_static_string<N, CharT, Traits>::size_type
+erase_if(
+    basic_static_string<N, CharT, Traits>& str,
+    UnaryPredicate pred)
+{
+  auto first = str.begin();
+  for (auto it = first; it != str.end(); ++it)
+    if (!pred(*it))
+      *first++ = std::move(*it);
+  const auto count = str.end() - first;
+  str.erase(first, str.end());
+  return count;
+}
+
 //------------------------------------------------------------------------------
 //
 // swap

test/static_string.cpp

@@ -16,6 +16,7 @@
 #include <boost/core/lightweight_test.hpp>
 #include <cstdlib>
 #include <cwchar>
+#include <cctype>
 #include <sstream>
 #include <string>
 
@@ -1848,6 +1849,51 @@ testErase()
     BOOST_TEST(testE(S("abcdefghijklmnopqrst"), 21, 0, S("can't happen")));
 }
 
+// done
+static
+void
+testEraseIf()
+{
+    // erase_if(static_string& str, UnaryPredicate pred)
+
+    {
+        static_string<3> s{""};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'a'; }) == 0);
+        BOOST_TEST(s == "");
+        BOOST_TEST(*s.end() == 0);
+    }
+    {
+        static_string<3> s{"aaa"};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'a'; }) == 3);
+        BOOST_TEST(s == "");
+        BOOST_TEST(*s.end() == 0);
+    }
+    {
+        static_string<3> s{"abc"};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'a'; }) == 1);
+        BOOST_TEST(s == "bc");
+        BOOST_TEST(*s.end() == 0);
+    }
+    {
+        static_string<3> s{"abc"};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'b'; }) == 1);
+        BOOST_TEST(s == "ac");
+        BOOST_TEST(*s.end() == 0);
+    }
+    {
+        static_string<3> s{"abc"};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'c'; }) == 1);
+        BOOST_TEST(s == "ab");
+        BOOST_TEST(*s.end() == 0);
+    }
+    {
+        static_string<3> s{"abc"};
+        BOOST_TEST(erase_if(s, [](char c) { return c == 'd'; }) == 0);
+        BOOST_TEST(s == "abc");
+        BOOST_TEST(*s.end() == 0);
+    }
+}
+
 // done
 static
 void
@@ -7171,6 +7217,7 @@ runTests()
   testClear();
   testInsert();
   testErase();
+  testEraseIf();
   testPushBack();
   testPopBack();
   testAppend();