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Requirements on keys for bulk visitation are overly restrictive

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp
Domain
backend

Research direction

Start by tracing the bulk visitation requirements for FwdIterator value types, key_type, Hash, and Pred in the unordered module. Check the existing tests or add focused coverage for keys implicitly convertible to key_type, and consider the work complete when that scenario is accepted without weakening the stated transparent-hash requirements.

Written by the indexing model from the issue text.

Description

Currently, bulk visitation requires that

[f]or K = std::iterator_traits::value_type, either K [be] key_type or else Hash::is_transparent and Pred::is_transparent [be] valid member typedefs.

This precludes the scenario where the keys are implicitly convertible to key_type, which seems to be overly restrictive. The drawback of allowing this is that conversion from std::iterator_traits<FwdIterator>::value_type to key_type will happen more than once for each key (twice, to be precise).

Dominant language
C++
Stars
92
Forks
88
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