[libcxx-commits] [libcxx] 8ca5830 - [libc++] Default the allocator argument for most string constructors (#169901)

[via libcxx-commits]

Author: Nikolas Klauser
Date: 2026-06-19T10:22:05-04:00
New Revision: 8ca5830992768650b77ee318dad5402108e8bed3

URL: https://github.com/llvm/llvm-project/commit/8ca5830992768650b77ee318dad5402108e8bed3
DIFF: https://github.com/llvm/llvm-project/commit/8ca5830992768650b77ee318dad5402108e8bed3.diff

LOG: [libc++] Default the allocator argument for most string constructors (#169901)

Allocators are generally very cheap to copy, so avoiding copies by
having separate overloads is not that useful. Defaulting them
significanlty reduces the overload set the compiler has to consider and
simplifies the code, since we can remove some functions in the future.

Closes #87368

Added: 
    

Modified: 
    libcxx/include/string

Removed: 
    


################################################################################
diff  --git a/libcxx/include/string b/libcxx/include/string
index a201d2ca44354..e5bc854cd34f3 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1003,15 +1003,9 @@ public:
   }
 #  endif // _LIBCPP_CXX03_LANG
 
-  template <__enable_if_t<__is_allocator_v<_Allocator>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* _LIBCPP_DIAGNOSE_NULLPTR __s) {
-    _LIBCPP_ASSERT_NON_NULL(__s != nullptr, "basic_string(const char*) detected nullptr");
-    __init(__s, traits_type::length(__s));
-  }
-
   template <__enable_if_t<__is_allocator_v<_Allocator>, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-  basic_string(const _CharT* _LIBCPP_DIAGNOSE_NULLPTR __s, const _Allocator& __a)
+  basic_string(const _CharT* _LIBCPP_DIAGNOSE_NULLPTR __s, const _Allocator& __a = _Allocator())
       : __alloc_(__a) {
     _LIBCPP_ASSERT_NON_NULL(__s != nullptr, "basic_string(const char*, allocator) detected nullptr");
     __init(__s, traits_type::length(__s));
@@ -1021,22 +1015,14 @@ public:
   basic_string(nullptr_t) = delete;
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s, size_type __n)
-      _LIBCPP_DIAGNOSE_NULLPTR_IF(__n != 0 && __s == nullptr, " if n is not zero") {
-    _LIBCPP_ASSERT_NON_NULL(__n == 0 || __s != nullptr, "basic_string(const char*, n) detected nullptr");
-    __init(__s, __n);
-  }
-
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-  basic_string(const _CharT* __s, size_type __n, const _Allocator& __a)
+  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s, size_type __n, const _Allocator& __a = _Allocator())
       _LIBCPP_DIAGNOSE_NULLPTR_IF(__n != 0 && __s == nullptr, " if n is not zero")
       : __alloc_(__a) {
     _LIBCPP_ASSERT_NON_NULL(__n == 0 || __s != nullptr, "basic_string(const char*, n, allocator) detected nullptr");
     __init(__s, __n);
   }
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(size_type __n, _CharT __c) { __init(__n, __c); }
-
 #  if _LIBCPP_STD_VER >= 23
   _LIBCPP_HIDE_FROM_ABI constexpr basic_string(
       basic_string&& __str, size_type __pos, const _Allocator& __alloc = _Allocator())
@@ -1059,7 +1045,8 @@ public:
 #  endif
 
   template <__enable_if_t<__is_allocator_v<_Allocator>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(size_type __n, _CharT __c, const _Allocator& __a)
+  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(size_type __n, _CharT __c, const _Allocator& __a = _Allocator())
       : __alloc_(__a) {
     __init(__n, __c);
   }
@@ -1098,29 +1085,16 @@ public:
             __enable_if_t<__can_be_converted_to_string_view_v<_CharT, _Traits, _Tp> &&
                               !is_same<__remove_cvref_t<_Tp>, basic_string>::value,
                           int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit basic_string(const _Tp& __t) {
-    __self_view __sv = __t;
-    __init(__sv.data(), __sv.size());
-  }
-
-  template <class _Tp,
-            __enable_if_t<__can_be_converted_to_string_view_v<_CharT, _Traits, _Tp> &&
-                              !is_same<__remove_cvref_t<_Tp>, basic_string>::value,
-                          int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit basic_string(const _Tp& __t, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit basic_string(const _Tp& __t, const allocator_type& __a = allocator_type())
       : __alloc_(__a) {
     __self_view __sv = __t;
     __init(__sv.data(), __sv.size());
   }
 
-  template <class _InputIterator, __enable_if_t<__has_input_iterator_category<_InputIterator>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(_InputIterator __first, _InputIterator __last) {
-    __init(__first, __last);
-  }
-
   template <class _InputIterator, __enable_if_t<__has_input_iterator_category<_InputIterator>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-  basic_string(_InputIterator __first, _InputIterator __last, const allocator_type& __a)
+  basic_string(_InputIterator __first, _InputIterator __last, const allocator_type& __a = allocator_type())
       : __alloc_(__a) {
     __init(__first, __last);
   }
@@ -1139,11 +1113,8 @@ public:
 #  endif
 
 #  ifndef _LIBCPP_CXX03_LANG
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(initializer_list<_CharT> __il) {
-    __init(__il.begin(), __il.end());
-  }
-
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(initializer_list<_CharT> __il, const _Allocator& __a)
+  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(initializer_list<_CharT> __il, const _Allocator& __a = _Allocator())
       : __alloc_(__a) {
     __init(__il.begin(), __il.end());
   }