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Section: 27.4.3.8.2 [string.find] Status: New Submitter: Jiang An Opened: 2025-05-07 Last modified: 2025-05-18
Priority: Not Prioritized
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Discussion:
P1206R7 added some requirements for sequence containers, including program-defined ones.
These requirements mean that if a custom C++20 sequence container type has no newly required member functions added in C++23 mode, it is no longer a sequence container, and uses of it withstd::stack, std::queue, or std::priority_queue possibly have undefined behavior or
make the program ill-formed. Additionally, some users want to use C++23 flat container adaptors
with old sequence containers (llvm/llvm-project#136656),
it is unclear whether such uses are intentionally rejected.
Perhaps the requirements on from_range_t constructor, insert_range and assign_range should be made optional,
although these operations should have specified semantics whenever being well-formed in immediate contexts.
Proposed resolution: