| Issue |
179139
|
| Summary |
[ADT] SmallSet is unusable in make_filter_range due to improper iterator facade usage
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Theodor
|
On a rather simple testcase attempt to iterate through "filtered" SmallSet fails on iterator dereference.
It tries to bind non-const reference to const value.
```
] cat test.cc
#include <llvm/ADT/SmallSet.h>
#include <llvm/ADT/STLExtras.h>
void test() {
llvm::SmallSet<int, 12> NewSet;
auto PredTrue = [](int A) { return true; };
auto Filtered = llvm::make_filter_range(NewSet, PredTrue);
for (const auto &Val : Filtered) {
(void)Val;
}
}
] gcc test.cc -I../llvm/include -I./include -std=c++17
In file included from ../llvm/include/llvm/ADT/SmallSet.h:21,
from test.cc:1:
../llvm/include/llvm/ADT/iterator.h: In instantiation of ‘ReferenceT llvm::iterator_adaptor_base<DerivedT, WrappedIteratorT, IteratorCategoryT, T, DifferenceTypeT, PointerT, ReferenceT>::operator*() const [with DerivedT = llvm::filter_iterator_base<llvm::SmallSetIterator<int, 12, std::less<int> >, test()::<lambda(int)>, std::forward_iterator_tag>; WrappedIteratorT = llvm::SmallSetIterator<int, 12, std::less<int> >; IteratorCategoryT = std::forward_iterator_tag; T = int; DifferenceTypeT = long int; PointerT = int*; ReferenceT = int&]’:
../llvm/include/llvm/ADT/STLExtras.h:471:28: required from ‘decltype(auto) llvm::filter_iterator_base<WrappedIteratorT, PredicateT, IterTag>::operator*() const [with WrappedIteratorT = llvm::SmallSetIterator<int, 12, std::less<int> >; PredicateT = test()::<lambda(int)>; IterTag = std::forward_iterator_tag]’
471 | return BaseT::operator*();
| ~~~~~~~~~~~~~~~~^~
test.cc:7:26: required from here
7 | for (const auto &Val : Filtered) {
| ^~~~~~~~
../llvm/include/llvm/ADT/iterator.h:305:42: error: binding reference of type ‘int&’ to ‘const int’ discards qualifiers
305 | ReferenceT operator*() const { return *I; }
| ^
```
This happens because SmallSetIterator fails to define its reference type as "const".
SmallSet does have const iterator by design, so SmallSetIterator should set ReferenceT parameter of its base class iterator_facade_base to "const T&".
I dont see an easy way to work around this issue.
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