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.

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, 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:

Dereferenceable iterators

Iterators for which the behavior of the expression *i is defined are called dereferenceable.

Iterators are not dereferenceable if.

• they are past-the-end iterators (including pointers past the end of an array) or before-begin iterators. Such iterators may be dereferenceable in a particular implementation, but the library never assumes that they are.
• they are singular iterators, that is, iterators that are not associated with any sequence. A null pointer, as well as a default-constructed pointer (holding an indeterminate value) is singular
• they were invalidated by one of the iterator-invalidating operations on the sequence to which they refer.

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