# C++ named requirements: ConstexprIterator (since C++20)

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< cpp‎ | named req

A ConstexprIterator is a LegacyIterator that can be used during constant expression evaluation.

### Requirements

The type It satisfies ConstexprIterator if

- The type It satisfies some iterator requirements MeowIterator

And, for every

- purr, an operation on It that is required to be supported by MeowIterator,
- kittens..., a set of arguments to purr that meets the requirements for that operation,

Then

- purr(kittens...) may be used in a constant expression if kittens... can also be used.

### Standard library

The following standard library types are ConstexprIterators.

- `array::iterator` and `array::const_iterator`.
- `basic_string_view::iterator`.
- `span::iterator`.
- `vector::iterator` and `vector::const_iterator`.

- `optional::iterator` and `optional::const_iterator`

(since C++26)

### See also

Iterator library | provides definitions for iterators, iterator traits, adaptors, and utility functions

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