In particular, improve the compile time of the overload set builder
that variant uses to determine which alternative to construct.
Instead of having the __overload type construct itself recursively,
this patch uses a flat construction for the overload set.
llvm-svn: 366033
The standard disallows narrowing conversions when constructing a variant.
This is checked by attempting to perform braced initialization of the
destination type from the argument type. However, braced initialization
can force the compiler (mostly clang) to eagerly instantiate the
constructors of the destintation type -- which can lead to errors in
a non-immediate context.
However, as variant is currently specified, the narrowing checks only
observably apply when the destination type is arithmetic. Meaning we can
skip the check for class types. Hense avoiding the hard errors.
In order to cause fewer build breakages, this patch avoids the narrowing
check except when the destination type is arithmetic.
llvm-svn: 366022
The paper P0608R3 - "A sane variant converting constructor" disallows
narrowing conversions in variant. It was meant to address this
surprising problem:
std::variant<std::string, bool> v = "abc";
assert(v.index() == 1); // constructs a bool.
However, it also disables every potentially narrowing conversion. For
example:
variant<unsigned> v = 0; // ill-formed
variant<string, double> v2 = 42; // ill-formed (int -> double narrows)
These latter changes break code. A lot of code. Within Google it broke
on the order of a hundred thousand target with thousands of root causes
responsible for the breakages.
Of the breakages related to the narrowing restrictions, none of them
exposed outstanding bugs. However, the breakages caused by boolean
conversions (~13 root causes), all but one of them were bugs.
For this reasons, I am adding a flag to disable the narrowing conversion
changes but not the boolean conversions one.
One purpose of this flag is to allow users to opt-out of breaking changes
in variant until the offending code can be cleaned up. For non-trivial
variant usages the amount of cleanup may be significant.
This flag is also required to support automated tooling, such as
clang-tidy, that can automatically fix code broken by this change.
In order for clang-tidy to know the correct alternative to construct,
it must know what alternative was being constructed previously, which
means running it over the old version of std::variant.
Because this change breaks so much code, I will be implementing the
aforementioned clang-tidy check in the very near future.
Additionally I'm plan present this new information to the committee so they can
re-consider if this is a breaking change we want to make.
I think libc++ should very seriously consider pulling this change
before the 9.0 release branch is cut. But that's a separate discussion
that I will start on the lists.
For now this is the minimal first step.
llvm-svn: 365960
to reflect the new license. These used slightly different spellings that
defeated my regular expressions.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351648
Summary:
P0602R4 makes the special member functions of optional and variant
conditionally trivial based on the types in the optional/variant.
We already implemented that, but the tests were organized as if this
were a non-standard extension. This patch reorganizes the tests in a
way that makes more sense since this is not an extension anymore.
Reviewers: EricWF, mpark, mclow.lists
Subscribers: christof, jkorous, dexonsmith, libcxx-commits
Differential Revision: https://reviews.llvm.org/D54772
llvm-svn: 350884
type.
Libc++ correctly asserts that a set of visitors for a variant all
return the same type. However, we use the visitation machinary to
perform relational operations. This causes a static assertion when
some of the alternatives relops return a UDT which is implicitly
convertible to bool instead of 'bool' exactly.
llvm-svn: 342560
This partially reverts commit r328261. The GCC bug has been fixed in
trunk and has never existed in a released version. Therefore the changes
to variant are unneeded.
However, the additional tests have been left in place.
llvm-svn: 328388
This patch works around variant test failures which are new to
GCC 8. GCC 8 either doesn't perform SFINAE in lexical order, or
it doesn't halt after encountering the first failure. This
causes hard error to occur instead of substitution failure.
See gcc.gnu.org/PR78489
llvm-svn: 328261
Summary:
Introduce a new form of `result_of` without function type encoding.
Rename and split `is_callable/is_nothrow_callable` into `is_invocable/is_nothrow_invocable/is_invocable_r/is_nothrow_invocable_r` (and associated types accordingly)
Change function type encoding of previous `is_callable/is_nothrow_callable` traits to conventional template type parameter lists.
Reviewers: EricWF, mclow.lists, bebuch
Reviewed By: EricWF, bebuch
Subscribers: lichray, bebuch, cfe-commits
Differential Revision: https://reviews.llvm.org/D38831
llvm-svn: 320509
Summary:
Currently `std::variant` always uses an unsigned int to store the variant index. However this isn't nessesary and causes `std::variant` to be larger than it needs to be in most cases.
This patch changes the index type to be `unsigned char` when possible, and `unsigned short` or `unsigned int` otherwise, depending on the size (Although it's questionable if it's even possible to create a variant with 65535 elements.
Unfortunately this change is an ABI break, and as such is only enabled in ABI v2.
Reviewers: mpark
Reviewed By: mpark
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D40210
llvm-svn: 318621
Remarks: This function shall not participate in overload resolution unless
`is_same_v<decay_t<T>, variant>` is false, unless `decay_t<T>` is
neither a specialization of `in_place_type_t` nor a specialization of
`in_place_index_t`, unless `is_constructible_v<Tj, T>` is true, and
unless the expression `FUN(std::forward<T>(t))` (with `FUN` being the
above-mentioned set of imaginary functions) is well formed.
Depends on D34111.
Reviewers: EricWF, K-ballo
Reviewed By: EricWF
Subscribers: fhahn
Differential Revision: https://reviews.llvm.org/D34112
llvm-svn: 305668
Summary:
- Removed the move-constructibe requirement from copy-assignable.
- Updated `__assign_alt` such that we direct initialize if
`_Tp` can be `nothrow`-constructible from `_Arg`, or `_Tp`'s
move construction can throw. Otherwise, construct a temporary and move it.
- Updated the tests to remove the pre-LWG2904 path.
Depends on D32671.
Reviewers: EricWF, CaseyCarter
Reviewed By: EricWF
Differential Revision: https://reviews.llvm.org/D33965
llvm-svn: 304891
This patch fixes the test failures and unexpected passes that occur
when testing against GCC 7. Specifically:
* don't mark __gcd as always inline because it's a recursive function. GCC diagnoses this.
* don't XFAIL the aligned allocation tests. GCC 7 supports them but not the -faligned-allocation option.
* Work around gcc.gnu.org/PR78489 in variants constructors.
llvm-svn: 302488
A static assertion was misfiring since it checked
is_callable<Visitor, decltype(__variant_alt<T>.value)>. However
the decltype expression doesn't capture the value category as
required. This patch applies extra braces to decltype to fix
that.
llvm-svn: 294612
Summary:
Exactly what the title says.
This patch also adds a `std::hash<nullptr_t>` specialization in C++17, but it was not added by this paper and I can't find the actual paper that adds it.
See http://wg21.link/P0513R0 for more info.
If there are no comments in the next couple of days I'll commit this
Reviewers: mclow.lists, K-ballo, EricWF
Reviewed By: EricWF
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D28938
llvm-svn: 292684
The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__type_visibility__)) with Clang. The only remaining difference
is that _LIBCPP_TYPE_VIS_ONLY can be applied to templates whereas
_LIBCPP_TYPE_VIS cannot (due to dllimport/dllexport not being allowed on
templates).
This patch renames _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS.
llvm-svn: 291035
These exception types are marked with `_LIBCPP_EXCEPTION_ABI` which
expands to `__attribute__((__visibility__("default")))` or
`__declspec(dllexport)`. When building for Windows, we would hit an
error:
cannot apply 'dllexport' to a 'dllexport' class
Remove the duplicate annotations as they will be inherited from the
class.
llvm-svn: 290785
Previously these hashes were 0 and -1 respectively. These seem like common
sentinel values and should be avoided to prevent needless collisions.
This patch changes those values to different arbitrary numbers, which should
hopefully cause less collisions. Because I couldn't help myself I choose the
fundamental constants for gravity and the speed of light.
llvm-svn: 288623
Eric Fiselier