Section: 24.3.1 [iterator.requirements.general] Status: C++20 Submitter: Daniel Krügler Opened: 2019-08-18 Last modified: 2021-02-25
Priority: 0
View all other issues in [iterator.requirements.general].
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Discussion:
The current definition of constexpr iterators is specified in 24.3.1 [iterator.requirements.general] p16 as follows:
Iterators are called constexpr iterators if all operations provided to meet iterator category requirements are constexpr functions, except for
(16.1) — a pseudo-destructor call (7.5.5.5 [expr.prim.id.dtor]), and
(16.2) — the construction of an iterator with a singular value.
With the acceptance of some proposals during the Cologne 2019 meeting, these additional requirements become mostly obsolete, as it had already been pointed out during that meeting:
With the acceptance of P0784R7, destructors can be declaredconstexpr and it is possible to perform a pseudo-destructor call within a
constant expression, so bullet (16.1) is no longer a necessary requirement.
With the acceptance of P1331R2, trivial default
initialization in constexpr contexts is now possible, and there is no longer a requirement
to initialize all sub-objects of a class object within a constant expression.
It seems to me that we should simply strike the above two constraining requirements of the
definition of constexpr iterators for C++20.
[2019-09-14 Issue Prioritization]
Status to Tentatively Ready and priority to 0 after five positive votes on the reflector.
Proposed resolution:
This wording is relative to N4830.
Modify 24.3.1 [iterator.requirements.general] as indicated:
-16- Iterators are called constexpr iterators if all operations provided to meet iterator category requirements are constexpr functions.
, except for
(16.1) — a pseudo-destructor call (7.5.5.5 [expr.prim.id.dtor]), and
(16.2) — the construction of an iterator with a singular value.