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libstdc++: Add static assertions for std::function requirements

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Add static assertions to std::function, so that more user-friendly
diagnostics are given when trying to store a non-copyable target object.

These preconditions were added as "Mandates:" by LWG 2447, but I'm
committing them separately from implementing that, to allow just this
change to be backported more easily.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/std_function.h (function::function(F)): Add
	static assertions to check constructibility requirements.
This commit is contained in:
Jonathan Wakely 2021-08-26 13:13:27 +01:00
parent 5889e842ae
commit 8cf428bfd3
1 changed files with 6 additions and 0 deletions
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6
libstdc++-v3/include/bits/std_function.h
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@ -422,6 +422,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
function(_Functor __f)
: _Function_base()
{
static_assert(is_copy_constructible<_Functor>::value,
"std::function target must be copy-constructible");
static_assert(is_constructible<_Functor, _Functor>::value,
"std::function target must be constructible from the "
"constructor argument");
using _My_handler = _Function_handler<_Res(_ArgTypes...), _Functor>;
if (_My_handler::_M_not_empty_function(__f))