3439. "Distance" template parameter is underspecified

Section: 24.4.3 [iterator.operations], 26.7.12 [alg.random.sample] Status: New Submitter: Jens Maurer Opened: 2020-05-01 Last modified: 2025-10-10

Priority: 3

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Discussion:

The library specification conveys pre-concept requirements on template parameters by naming, e.g. "InputIterator".

There is no general specification for template parameters named "Distance", as used by std::advance (see 24.4.3 [iterator.operations]). When addressing this omission, the local restriction in 26.7.12 [alg.random.sample] could possibly be removed.

See the related issue 3213 for the Size template parameter.

[2025-10-10; Jonathan comments]

The SGI STL has the requirement that "Distance is an integral type that is convertible to InputIterator's distance type." But the SGI STL also required that Size arguments to fill_n etc. have integral types, and the standard only requires them to be convertible to integral types. Presumably that relaxation was intentional.

[2020-05-09; Reflector prioritization]

Set priority to 3 after reflector discussions.

Proposed resolution: