https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71788
Bug ID: 71788
Summary: is_trivially_copy_constructible gives false for types
with user defined destructors
Product: gcc
Version: 5.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: bplusplus at hotmail dot com
Target Milestone: ---
Given the type
struct Tp
{
Tp() = default;
Tp(const Tp&) = default;
Tp(Tp&&) = default;
~Tp() {}
};
The following static asserts fail
static_assert(std::is_trivially_copy_constructible<Tp>::value, "");
static_assert(std::is_trivially_move_constructible<Tp>::value, "");
If the destructor is defaulted (or removed, such that it is implicitly
generated), the asserts do not trigger.
I'm not entirely sure this is a bug, but as far as I can determine from the
standard, it is. Relevant text (ยง12.8 [class.copy], paragraph 12):
"A copy/move constructor for class X is trivial if it is not user-provided, its
parameter-type-list is equivalent to the parameter-type-list of an implicit
declaration, and if
- class X has no virtual functions (10.3) and no virtual base classes (10.1),
and
- class X has no non-static data members of volatile-qualified type, and
- the constructor selected to copy/move each direct base class subobject is
trivial, and
- for each non-static data member of X that is of class type (or array
thereof), the constructor selected to copy/move that member is trivial;
otherwise the copy/move constructor is non-trivial."
No mention that a user defined destructor should make either copy or move
constructors non-trivial if they otherwise qualify. Additionally, using the old
std::has_trivial_copy_constructor (and the built-in __has_trivial_copy it's
based on) does not trigger the assert.
