https://llvm.org/bugs/show_bug.cgi?id=28412
Bug ID: 28412
Summary: std::vector incorrectly requires CopyConstructible,
Destructible and other concepts
Product: libc++
Version: unspecified
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: zi...@kayari.org
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
Classification: Unclassified
Container requirements are all stated in terms of CopyInsertable into X, and
Erasable from X, which involves indirection through the container's allocator.
The following test shows a class which can only be constructed/destroyed by its
allocator, revealing that std::vector tries to construct temporaries directly
without going through the allocator.
/usr/local/libcxx-head/include/c++/v1/vector:1815:24: error: call to deleted
constructor of 'value_type' (aka 'X')
#include <vector>
struct Tag { };
template<typename T>
class TaggingAllocator
{
public:
using value_type = T;
TaggingAllocator() = default;
template<typename U>
TaggingAllocator(const TaggingAllocator<U>&) { }
T*
allocate(std::size_t n) { return std::allocator<T>{}.allocate(n); }
void
deallocate(T* p, std::size_t n) { std::allocator<T>{}.deallocate(p, n); }
template<typename U, typename... Args>
void
construct(U* p, Args&&... args)
{ ::new((void*)p) U(Tag{}, std::forward<Args>(args)...); }
template<typename U, typename... Args>
void
destroy(U* p)
{ p->~U(); }
};
template<typename T, typename U>
bool
operator==(const TaggingAllocator<T>&, const TaggingAllocator<U>&)
{ return true; }
template<typename T, typename U>
bool
operator!=(const TaggingAllocator<T>&, const TaggingAllocator<U>&)
{ return false; }
struct X
{
// All constructors must be passed the Tag type.
// DefaultInsertable into vector<X, TaggingAllocator<X>>,
X(Tag) { }
// CopyInsertable into vector<X, TaggingAllocator<X>>,
X(Tag, const X&) { }
// MoveInsertable into vector<X, TaggingAllocator<X>>, and
X(Tag, X&&) { }
// EmplaceConstructible into vector<X, TaggingAllocator<X>> from args.
template<typename... Args>
X(Tag, Args&&...) { }
// not DefaultConstructible, CopyConstructible or MoveConstructible.
X() = delete;
X(const X&) = delete;
X(X&&) = delete;
// CopyAssignable.
X& operator=(const X&) { return *this; }
// MoveAssignable.
X& operator=(X&&) { return *this; }
private:
// Not Destructible.
~X() { }
// Erasable from vector<X, TaggingAllocator<X>>.
friend class TaggingAllocator<X>;
};
int main()
{
std::vector<X, TaggingAllocator<X>> v;
v.reserve(3);
v.emplace_back();
v.emplace(v.begin());
v.emplace(v.begin(), 1, 2, 3);
}
// template class std::vector<X, TaggingAllocator<X>>;
Uncommenting the last line to explicitly instantiate the vector fails
differently, presumably there are some SFINAE conditions which make invalid
assumptions about the type.
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