As mentioned in https://discourse.llvm.org/t/rfc-extend-ranges-infrastructure-to-better-match-c-20/65377
Lambda objects are not copy assignable, and therefore neither are
iterator types which hold a lambda. STL code require iterators be
copy assignable. Users may not use mapped_iterator with a std::deque
for example: https://godbolt.org/z/4Px7odEEd
This blog post [1] explains the problem and solution. We define a
wrapper class to store callable objects with two specialization.
1. Specialization for non-function types
- Use a std::optional as storage for non-function callable.
- Define operator=() implementation(s) which use
std::optional::emplace() instead of the assignment operator.
2. Specialization for function types
- Store as a pointer (even if template argument is a function reference).
- Default construct pointer to nullptr.
This Callable wrapper class is now default constructible (with invalid
state) and copy/move assignable.
With these new properties available on the callable object,
mapped_iterator can define a default constructor as well.
[1] https://www.fluentcpp.com/2019/04/16/an-alternative-design-to-iterators-and-ranges-using-stdoptional/
Reviewed By: kazu
Differential Revision: https://reviews.llvm.org/D134675
mapped_iterator is a useful abstraction for applying a
map function over an existing iterator, but our current
usage ends up allocating storage/making indirect calls
even with the map function is a known function, which
is horribly inefficient. This commit refactors the usage
of mapped_iterator to avoid this, and allows for directly
referencing the map function when dereferencing.
Fixes PR52319
Differential Revision: https://reviews.llvm.org/D113511
to reflect the new license.
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: 351636
Summary:
This eliminates the boilerplate implementation of the iterator interface in
mapped_iterator.
This patch also adds unit tests that verify that the mapped function is applied
by operator* and operator->, and that references returned by the map function
are returned via operator*.
Reviewers: dblaikie, chandlerc
Subscribers: llvm-commits, mgorny
Differential Revision: https://reviews.llvm.org/D39855
llvm-svn: 317902
MSVC as usual:
C:\Buildbot\Slave\llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast\llvm.src\include\llvm/ADT/STLExtras.h(120):
error C2100: illegal indirection
C:\Buildbot\Slave\llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast\llvm.src\include\llvm/IR/Instructions.h(3966):
note: see reference to class template instantiation
'llvm::mapped_iterator<llvm::User::op_iterator,llvm::CatchSwitchInst::DerefFnTy>'
being compiled
This reverts commit e091dd63f1f34e043748e28ad160d3bc17731168.
llvm-svn: 263760
Simon Pilgrim