This is something like nullopt in std::experimental::optional. Optional
could already be constructed from None, so this seems like an obvious
extension from there.
I have a use in a future patch for Clang, though it may not go that
way/end up used - so this seemed worth committing now regardless.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245518 91177308-0d34-0410-b5e6-96231b3b80d8
This can be used for in-place initialization of non-moveable types.
For compilers that don't support variadic templates, only up to four
arguments are supported. We can always add more, of course, but this
should be good enough until we move to a later MSVC that has full
support for variadic templates.
Inspired by std::experimental::optional from the "Library Fundamentals" C++ TS.
Reviewed by David Blaikie.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218732 91177308-0d34-0410-b5e6-96231b3b80d8
This takes a single argument convertible to T, and
- if the Optional has a value, returns the existing value,
- otherwise, constructs a T from the argument and returns that.
Inspired by std::experimental::optional from the "Library Fundamentals" C++ TS.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218618 91177308-0d34-0410-b5e6-96231b3b80d8
This generalizes Optional to require less from the T type by using aligned
storage for backing & placement new/deleting the T into it when necessary.
Also includes unit tests.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175580 91177308-0d34-0410-b5e6-96231b3b80d8
