Re: [committed] libstdc++: Add default constructor to net::service_already_exists (PR 94199)

[Jonathan Wakely via Gcc-patches]

On 16/03/20 22:54 +0000, Jonathan Wakely wrote:

The service_already_exists exception type specified in the TS doesn't
have any constructors defined. Since its base class isn't default
constructible, that means has no usable constructors. This may be a
defect in the TS.

This patch fixes it by adding a default constructor, but making it
private. The make_service function is declared as a friend to be able to
call that private constructor.

        PR libstdc++/94199
        * include/experimental/executor (service_already_exists): Add default
        constructor. Declare make_service to be a friend.
        * testsuite/experimental/net/execution_context/make_service.cc: New
        test.

LWG preferred to make the constrcutor public, so this patch does that.

Tested x86_64-linux, committed to master.



commit 00082ff88cf4e25fc1041e9effd1c92fbaaa8d62
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Apr 24 14:15:51 2020 +0100

    libstdc++: Make net::service_already_exists default constructible
    
    The LWG issue I created is Tentatively Ready and proposes to declare a
    public default constructor, rather than the private one I added
    recently.
    
            * include/experimental/executor (service_already_exists): Make default
            constructor public (LWG 3414).
            * testsuite/experimental/net/execution_context/make_service.cc: Check
            the service_already_exists can be default constructed.

diff --git a/libstdc++-v3/include/experimental/executor b/libstdc++-v3/include/experimental/executor
index fa39eaa0468..3560e345e8a 100644
--- a/libstdc++-v3/include/experimental/executor
+++ b/libstdc++-v3/include/experimental/executor
@@ -129,10 +129,9 @@ inline namespace v1
 
   class service_already_exists : public logic_error
   {
-    template<typename _Service, typename... _Args>
-      friend _Service&
-      make_service(execution_context&, _Args&&...);
-
+  public:
+    // _GLIBCXX_RESOLVE_LIB_DEFECTS
+    // 3414. service_already_exists has no usable constructors
     service_already_exists() : logic_error("service already exists") { }
   };
 
diff --git a/libstdc++-v3/testsuite/experimental/net/execution_context/make_service.cc b/libstdc++-v3/testsuite/experimental/net/execution_context/make_service.cc
index f134add48b5..0898d12927a 100644
--- a/libstdc++-v3/testsuite/experimental/net/execution_context/make_service.cc
+++ b/libstdc++-v3/testsuite/experimental/net/execution_context/make_service.cc
@@ -34,3 +34,6 @@ void test01(net::execution_context& c)
 {
   net::make_service<S>(c);
 }
+
+static_assert(std::is_default_constructible<net::service_already_exists>(),
+	      "LWG 3414. service_already_exists has no usable constructors");