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[C++ PATCH] P0624R2 - Default constructible and assignable stateless lambdas
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jason Merrill <jason at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 14 Jun 2018 15:00:06 +0200
- Subject: [C++ PATCH] P0624R2 - Default constructible and assignable stateless lambdas
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
Hi!
The following patch implements P0624R2, where stateless lambdas don't have
deleted default ctor and copy assignment operator anymore.
Tested on x86_64-linux with check-c++-all and libstdc++ testsuite, ok for
trunk?
2018-06-14 Jakub Jelinek <jakub@redhat.com>
P0624R2 - Default constructible and assignable stateless lambdas
* method.c (synthesized_method_walk): For C++2a don't mark
sfk_constructor or sfk_copy_assignment as deleted if lambda has
no lambda-captures.
* g++.dg/cpp2a/lambda1.C: New test.
* g++.dg/cpp0x/lambda/lambda-ice2.C: Adjust expected diagnostics
for -std=c++2a.
--- gcc/cp/method.c.jj 2018-05-21 13:15:33.519575351 +0200
+++ gcc/cp/method.c 2018-06-14 13:48:58.825585083 +0200
@@ -1539,10 +1539,15 @@ synthesized_method_walk (tree ctype, spe
{
/* "The closure type associated with a lambda-expression has a deleted
default constructor and a deleted copy assignment operator."
- This is diagnosed in maybe_explain_implicit_delete. */
+ This is diagnosed in maybe_explain_implicit_delete.
+ In C++2a, only lambda-expressions with lambda-captures have those
+ deleted. */
if (LAMBDA_TYPE_P (ctype)
- && (sfk == sfk_constructor
- || sfk == sfk_copy_assignment))
+ && (sfk == sfk_constructor || sfk == sfk_copy_assignment)
+ && (cxx_dialect < cxx2a
+ || LAMBDA_EXPR_CAPTURE_LIST (CLASSTYPE_LAMBDA_EXPR (ctype))
+ || LAMBDA_EXPR_DEFAULT_CAPTURE_MODE
+ (CLASSTYPE_LAMBDA_EXPR (ctype)) != CPLD_NONE))
{
*deleted_p = true;
return;
--- gcc/testsuite/g++.dg/cpp2a/lambda1.C.jj 2018-06-14 14:27:29.903602374 +0200
+++ gcc/testsuite/g++.dg/cpp2a/lambda1.C 2018-06-14 14:26:51.462571226 +0200
@@ -0,0 +1,58 @@
+// P0624R2
+// { dg-do compile { target c++11 } }
+
+#if __cplusplus >= 201402L
+#define A auto
+#else
+#define A int
+#endif
+
+void
+f1 ()
+{
+ auto greater = [](A x, A y) { return x > y; }; // { dg-message "a lambda closure type has a deleted (default constructor|copy assignment operator)" "" { target c++17_down } }
+ decltype (greater) gt; // { dg-error "use of deleted function" "" { target c++17_down } }
+ gt = greater; // { dg-error "use of deleted function" "" { target c++17_down } }
+}
+
+void
+f2 ()
+{
+ auto greater = [&](A x, A y) { return x > y; }; // { dg-message "a lambda closure type has a deleted (default constructor|copy assignment operator)" }
+ decltype (greater) gt; // { dg-error "use of deleted function" }
+ gt = greater; // { dg-error "use of deleted function" }
+}
+
+void
+f3 ()
+{
+ auto greater = [=](A x, A y) { return x > y; }; // { dg-message "a lambda closure type has a deleted (default constructor|copy assignment operator)" }
+ decltype (greater) gt; // { dg-error "use of deleted function" }
+ gt = greater; // { dg-error "use of deleted function" }
+}
+
+void
+f4 (int i)
+{
+ auto greater = [i](A x, A y) { return x > y; }; // { dg-message "a lambda closure type has a deleted (default constructor|copy assignment operator)" }
+ decltype (greater) gt; // { dg-error "use of deleted function" }
+ gt = greater; // { dg-error "use of deleted function" }
+}
+
+#if __cplusplus > 201703L
+void
+f5 ()
+{
+ auto greater = [](auto x, auto y) constexpr { return x > y; };
+ decltype (greater) gt;
+ static_assert (!gt (1, 2));
+ static_assert (gt (4, 3));
+ static_assert (!gt (3.5, 3.75));
+ static_assert (gt (3.5, 3.25));
+ gt = greater;
+ static_assert (!gt (1, 2));
+ static_assert (gt (4, 3));
+ static_assert (!gt (3.5, 3.75));
+ static_assert (gt (3.5, 3.25));
+}
+#endif
--- gcc/testsuite/g++.dg/cpp0x/lambda/lambda-ice2.C.jj 2014-05-15 11:58:42.000000000 +0200
+++ gcc/testsuite/g++.dg/cpp0x/lambda/lambda-ice2.C 2018-06-14 14:32:03.760824236 +0200
@@ -2,15 +2,15 @@
// { dg-do compile { target c++11 } }
template<typename F>
-decltype(F()) run(F f) // { dg-message "note" }
+decltype(F()) run(F f) // { dg-message "note" "" { target c++17_down } }
{
- return f();
+ return f(); // { dg-error "could not convert" "" { target c++2a } }
}
int main()
{
- auto l = []() { return 5; }; // { dg-message "lambda closure type" }
+ auto l = []() { return 5; }; // { dg-message "lambda closure type" "" { target c++17_down } }
- run(l); // { dg-error "no match" }
- // { dg-error "use of deleted function" "candidate explanation" { target *-*-* } 5 }
+ run(l); // { dg-error "no match" "" { target c++17_down } }
+ // { dg-error "use of deleted function" "candidate explanation" { target c++17_down } 5 }
}
Jakub