C++ named requirements: LegacyIterator

The LegacyIterator requirements describe types that can be used to identify and traverse the elements of a container.

LegacyIterator is the base set of requirements used by other iterator types: LegacyInputIterator, LegacyOutputIterator, LegacyForwardIterator, LegacyBidirectionalIterator, and LegacyRandomAccessIterator. Iterators can be thought of as an abstraction of pointers.

All the categories of iterators require only those functions that are realizable for a given category in constant time (amortized). Therefore, requirement tables and concept definitions (since C++20)for the iterators do not specify complexity.

Requirements

The type It satisfies LegacyIterator if.

• The type It satisfies CopyConstructible, and
• The type It satisfies CopyAssignable, and
• The type It satisfies Destructible, and
• lvalues of type It satisfy Swappable, and
• std::iterator_traits<It> has member typedefs value_type (until C++20), difference_type, reference, pointer, and iterator_category , and
• Given r, an lvalue of type It, the following expressions must be valid and have their specified effects:

template<class I>
concept __LegacyIterator =
    requires(I i)
    {
        {   *i } -> __Referenceable;
        {  ++i } -> std::same_as<I&>;
        { *i++ } -> __Referenceable;
    } && std::copyable<I>;

Defect Reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also