Libc++ has to deduce the 'allocator_arg_t' parameter as 'AllocArgT' for the
following constructor:
template <class Alloc> tuple(allocator_arg_t, Alloc const&)
Previously libc++ has tried to support tags derived from 'allocator_arg_t' by
using 'is_base_of<AllocArgT, allocator_arg_t>'. However this breaks whenever a
2-tuple contains a reference to an incomplete type as its first parameter.
See https://llvm.org/bugs/show_bug.cgi?id=27684
llvm-svn: 273334
There are two main fixes in this patch.
First the constructor SFINAE was changed so that it's evaluated in two stages
where the first stage evaluates the "safe" SFINAE conditions and the second
evaluates the "dangerous" ones. The key is that the second stage is lazily
evaluated only if the first stage passes. This helps fix PR23256
(https://llvm.org/bugs/show_bug.cgi?id=23256).
The second fix is for PR22806 and LWG issue 2549. This fix applies
the suggested resolution to the LWG issue in order to prevent the construction
of dangling references. The SFINAE for this check is contained within
the _PreferTupleLikeConstructor alias template. The tuple-like constructors
are disabled whenever that trait returns false.
(https://llvm.org/bugs/show_bug.cgi?id=22806)
(http://cplusplus.github.io/LWG/lwg-active.html#2549)
llvm-svn: 266461
Summary:
A default uses-allocator constructor has been added since that overload was previously provided by the extended constructor.
Since Clang does implicit conversion checking after substitution this constructor has to deduce the allocator_arg_t parameter so that it can prevent the evaluation of "is_default_constructible" if the first argument doesn't match. See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1391 for more information.
This patch fixes PR24779 (https://llvm.org/bugs/show_bug.cgi?id=24779)
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D19006
llvm-svn: 266409
Summary: Currently we only enable the use of __is_final(...) with Clang. GCC also provides __is_final(...) since 4.7 in all standard modes. This patch creates the macro _LIBCPP_HAS_IS_FINAL to note the availability of `__is_final`.
Reviewers: danalbert, mclow.lists
Reviewed By: mclow.lists
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D8795
llvm-svn: 239664
Summary:
Currently parts of the SFINAE on tuples default constructor always gets evaluated even when the default constructor is never called or instantiated. This can cause a hard compile error when a tuple is created with types that do not have a default constructor. Below is a self contained example using a pair like class. This code will not compile but probably should.
```
#include <type_traits>
template <class T>
struct IllFormedDefaultImp {
IllFormedDefaultImp(T x) : value(x) {}
constexpr IllFormedDefaultImp() {}
T value;
};
typedef IllFormedDefaultImp<int &> IllFormedDefault;
template <class T, class U>
struct pair
{
template <bool Dummy = true,
class = typename std::enable_if<
std::is_default_constructible<T>::value
&& std::is_default_constructible<U>::value
&& Dummy>::type
>
constexpr pair() : first(), second() {}
pair(T const & t, U const & u) : first(t), second(u) {}
T first;
U second;
};
int main()
{
int x = 1;
IllFormedDefault v(x);
pair<IllFormedDefault, IllFormedDefault> p(v, v);
}
```
One way to fix this is to use `Dummy` in a more involved way in the constructor SFINAE. The following patch fixes these sorts of hard compile errors for tuple.
Reviewers: mclow.lists, rsmith, K-ballo, EricWF
Reviewed By: EricWF
Subscribers: ldionne, cfe-commits
Differential Revision: http://reviews.llvm.org/D7569
llvm-svn: 230120
Eric Fiselier