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[v3] Support allocators in tuples of zero size.

Message ID CAFk2RUZJVkONk+o=ickt5PDb76ZJheP+W=PhDnMQg2fph7ZdyQ@mail.gmail.com
State New
Headers show

Commit Message

Ville Voutilainen June 5, 2016, 6:15 p.m. UTC 
On 5 June 2016 at 20:59, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
> All in all this is a bit inane, but the spec requires a zero-sized tuple
> to provide allocator overloads for constructors, even though they do
> absolutely nothing (they completely ignore the allocator). Presumably
> these are also useful for some metaprogrammers I haven't heard of.
> This takes us one small step further to pass libc++'s testsuite for tuple.
>
> Tested on Linux-X64.
>
> 2016-06-05  Ville Voutilainen  <ville.voutilainen@gmail.com>
>
>     Support allocators in tuples of zero size.
>     * include/std/tuple (tuple<>::tuple(),
>     tuple<>::tuple(allocator_arg_t, const _Alloc&),
>     tuple<>::tuple(allocator_arg_t, const _Alloc&, const tuple&),
>     tuple<>::tuple(allocator_arg_t, const _Alloc&, tuple&&)): New.
>     * testsuite/20_util/tuple/cons/allocators.cc: Adjust.

Uh, perhaps we shouldn't add a useless move constructor.

2016-06-05  Ville Voutilainen  <ville.voutilainen@gmail.com>

    Support allocators in tuples of zero size.
    * include/std/tuple (tuple<>::tuple(),
    tuple<>::tuple(allocator_arg_t, const _Alloc&),
    tuple<>::tuple(allocator_arg_t, const _Alloc&, const tuple&)): New.
    * testsuite/20_util/tuple/cons/allocators.cc: Adjust.

Comments

Jonathan Wakely June 6, 2016, 4:11 p.m. UTC | #1 
On 05/06/16 21:15 +0300, Ville Voutilainen wrote:
>     {
>     public:
>       void swap(tuple&) noexcept { /* no-op */ }
>+      // We need the default since we're going to define no-op
>+      // allocator constructors.
>+      tuple() = default;
>+      // No-op allocator constructors.
>+      template<typename _Alloc>
>+	tuple(allocator_arg_t __tag, const _Alloc& __a) { }
>+      template<typename _Alloc>
>+	tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in) { }

Please remove the names of the unused parameters, so we don't get
warnings with -Wsystem-headers -Wunused-parameter.

OK with that change, thanks.
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Patch

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 17c8204..7570883 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -876,6 +876,14 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
     public:
       void swap(tuple&) noexcept { /* no-op */ }
+      // We need the default since we're going to define no-op
+      // allocator constructors.
+      tuple() = default;
+      // No-op allocator constructors.
+      template<typename _Alloc>
+	tuple(allocator_arg_t __tag, const _Alloc& __a) { }
+      template<typename _Alloc>
+	tuple(allocator_arg_t __tag, const _Alloc& __a, const tuple& __in) { }
     };
 
   /// Partial specialization, 2-element tuple.
diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/allocators.cc b/libstdc++-v3/testsuite/20_util/tuple/cons/allocators.cc
index 052b79f..bc45780 100644
--- a/libstdc++-v3/testsuite/20_util/tuple/cons/allocators.cc
+++ b/libstdc++-v3/testsuite/20_util/tuple/cons/allocators.cc
@@ -162,8 +162,30 @@  void test01()
 
 }
 
+void test02()
+{
+  bool test __attribute__((unused)) = true;
+  using std::allocator_arg;
+  using std::tuple;
+  using std::make_tuple;
+
+  typedef tuple<> test_type;
+
+  MyAlloc a;
+
+  // default construction
+  test_type t1(allocator_arg, a);
+  // copy construction
+  test_type t2(allocator_arg, a, t1);
+  // move construction
+  test_type t3(allocator_arg, a, std::move(t1));
+  // make_tuple
+  test_type empty = make_tuple();
+}
+
 int main()
 {
   test01();
+  test02();
   return 0;
 }