Patchwork [v3] constrain std::function constructor to only accept callable types

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Submitter Jonathan Wakely
Date April 29, 2012, 11:16 p.m.
Message ID <CAH6eHdToKoXGtZsvmhkpno6raXgzmY=T5eRwR1WAunQ9D_XWvw@mail.gmail.com>
Download mbox | patch
Permalink /patch/155777/
State New
Headers show

Comments

Jonathan Wakely - April 29, 2012, 11:16 p.m.
Currently we only constrain std::function's constructor to reject
integral arguments, this patch changes it to reject non-callable
arguments.  This is the proposed resolution of LWG 2132, I had already
planned to do this anyway before the issue was opened so I don't see
any need to wait for a DR.

        * include/std/functional (function::function(F)): LWG 2132: Disable
        constructor if argument isn't callable.
        * testsuite/20_util/function/cons/callable.cc: New.

Tested x86_64-linux, committed to trunk.
commit 0e069c4221d6ed4fda7d10938470c472170dcad7
Author: Jonathan Wakely <jwakely.gcc@gmail.com>
Date:   Tue Feb 14 22:22:48 2012 +0000

    	* include/std/functional (function::function(F)): LWG 2132: Disable
    	constructor if argument isn't callable.
    	* testsuite/20_util/function/cons/callable.cc: New.

Patch

diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index 980c6ab..0edb4f1 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -1856,7 +1856,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
       {
 	typedef _Function_base::_Base_manager<_Functor*> _Base;
 
-    public:
+      public:
 	static bool
 	_M_manager(_Any_data& __dest, const _Any_data& __source,
 		   _Manager_operation __op)
@@ -1994,7 +1994,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
       typedef _Simple_type_wrapper<_Functor> _Wrapper;
       typedef _Function_base::_Base_manager<_Wrapper> _Base;
 
-     public:
+    public:
       static bool
       _M_manager(_Any_data& __dest, const _Any_data& __source,
 		 _Manager_operation __op)
@@ -2038,7 +2038,23 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
     {
       typedef _Res _Signature_type(_ArgTypes...);
 
-      struct _Useless { };
+      template<typename _Functor>
+	using _Invoke = decltype(__callable_functor(std::declval<_Functor&>())
+				 (std::declval<_ArgTypes>()...) );
+
+      template<typename _CallRes, typename _Res1>
+	struct _CheckResult
+	: is_convertible<_CallRes, _Res1> { };
+
+      template<typename _CallRes>
+	struct _CheckResult<_CallRes, void>
+	: true_type { };
+
+      template<typename _Functor>
+	using _Callable = _CheckResult<_Invoke<_Functor>, _Res>;
+
+      template<typename _Cond, typename _Tp>
+	using _Requires = typename enable_if<_Cond::value, _Tp>::type;
 
     public:
       typedef _Res result_type;
@@ -2099,11 +2115,9 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
        *  If @a __f is a non-NULL function pointer or an object of type @c
        *  reference_wrapper<F>, this function will not throw.
        */
-      template<typename _Functor>
-	function(_Functor __f,
-		 typename enable_if<
-			   !is_integral<_Functor>::value, _Useless>::type
-		   = _Useless());
+      template<typename _Functor,
+	       typename = _Requires<_Callable<_Functor>, void>>
+	function(_Functor);
 
       /**
        *  @brief %Function assignment operator.
@@ -2178,7 +2192,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
        *  reference_wrapper<F>, this function will not throw.
        */
       template<typename _Functor>
-	typename enable_if<!is_integral<_Functor>::value, function&>::type
+	_Requires<_Callable<_Functor>, function&>
 	operator=(_Functor&& __f)
 	{
 	  function(std::forward<_Functor>(__f)).swap(*this);
@@ -2187,7 +2201,7 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
 
       /// @overload
       template<typename _Functor>
-	typename enable_if<!is_integral<_Functor>::value, function&>::type
+	function&
 	operator=(reference_wrapper<_Functor> __f) noexcept
 	{
 	  function(__f).swap(*this);
@@ -2294,11 +2308,9 @@  _GLIBCXX_HAS_NESTED_TYPE(result_type)
     }
 
   template<typename _Res, typename... _ArgTypes>
-    template<typename _Functor>
+    template<typename _Functor, typename>
       function<_Res(_ArgTypes...)>::
-      function(_Functor __f,
-	       typename enable_if<
-			!is_integral<_Functor>::value, _Useless>::type)
+      function(_Functor __f)
       : _Function_base()
       {
 	typedef _Function_handler<_Signature_type, _Functor> _My_handler;
diff --git a/libstdc++-v3/testsuite/20_util/function/cons/callable.cc b/libstdc++-v3/testsuite/20_util/function/cons/callable.cc
new file mode 100644
index 0000000..209c404
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/function/cons/callable.cc
@@ -0,0 +1,51 @@ 
+// { dg-options "-std=gnu++0x" }
+// { dg-do compile }
+
+// Copyright (C) 2012 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <functional>
+#include <testsuite_hooks.h>
+
+void* f(std::function<void()>) { return nullptr; }
+int f(std::function<void(int)>) { return 1; }
+
+void test01()
+{
+  void* p __attribute__((unused));
+  int i __attribute__((unused));
+
+  p = f([] { });
+  i = f([] (int) { });
+}
+
+void g(std::function<void()>) { }
+void h(std::function<int(int)>) { }
+
+void test02()
+{
+  g([] { return "ignored"; });
+  h([] (char c) { return c; });
+}
+
+int main()
+{
+  test01();
+  test02();
+
+  return 0;
+}