C++ named requirements: LegacyRandomAccessIterator

 

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C++ named requirements

Basic
DefaultConstructible CopyAssignable CopyConstructible	MoveAssignable (C++11) MoveConstructible (C++11) Destructible
Type properties
ScalarType TriviallyCopyable (C++11) StandardLayoutType (C++11)	PODType TrivialType (C++11) ImplicitLifetimeType (C++20)
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EqualityComparable LessThanComparable Swappable (C++11) ValueSwappable (C++11) NullablePointer (C++11) Hash (C++11)	Allocator FunctionObject Callable Predicate BinaryPredicate Compare
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DefaultInsertable (C++11) CopyInsertable (C++11) MoveInsertable (C++11)	EmplaceConstructible (C++11) Erasable (C++11)
Iterator
LegacyIterator LegacyOutputIterator LegacyInputIterator LegacyForwardIterator	LegacyBidirectionalIterator LegacyRandomAccessIterator LegacyContiguousIterator (C++17) ConstexprIterator (C++20)
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FormattedInputFunction UnformattedInputFunction	FormattedOutputFunction UnformattedOutputFunction
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Other
CharTraits RegexTraits (C++11) BitmaskType NumericType LiteralType (C++11)	UnaryTypeTrait (C++11) BinaryTypeTrait (C++11) TransformationTrait (C++11) Clock (C++11) TrivialClock (C++11)

 

A LegacyRandomAccessIterator is a LegacyBidirectionalIterator that can be moved to point to any element in constant time.

If a LegacyRandomAccessIterator it originates from a Container, then it's value_type is the same as the container's, so dereferencing (*it) obtains the container's value_type.

A pointer to an element of an array satisfies all requirements of LegacyRandomAccessIterator

Requirements

The type It satisfies LegacyRandomAccessIterator if

• The type It satisfies LegacyBidirectionalIterator

And, given

• value_type, the type denoted by std::iterator_traits<It>::value_type
• difference_type, the type denoted by std::iterator_traits<It>::difference_type
• reference, the type denoted by std::iterator_traits<It>::reference
• i, a, b, objects of type It or const It
• r, a value of type It&
• n, an integer of type difference_type

The following expressions must be valid and have their specified effects

Expression	Return type	Operational semantics	Notes
r += n	It&	difference_type m = n; if (m >= 0) while (m--) ++r; else while (m++) --r; return r;	n can be both positive or negative The complexity is constant (that is, the implementation cannot actually execute the while loop shown in operational semantics)
a + n n + a	It	It temp = a; return temp += n;	n can be both positive or negative a + n == n + a
r -= n	It&	return r += -n;	The absolute value of n must be within the range of representable values of difference_type.
i - n	It	It temp = i; return temp -= n;
b - a	difference_type	return n;	Precondition: there exists a value n of type difference_type such that a+n==b Postcondition: b == a + (b - a).
i[n]	convertible to reference	*(i + n)
a < b	contextually convertible to bool	Equivalent to return b - a > 0;	Precondition: same as of b - a Strict total ordering relation: !(a < a) if a < b then !(b < a) if a < b and b < c then a < c a < b or b < a or a == b (exactly one of the expressions is true)
a > b	contextually convertible to bool	b < a	Total ordering relation opposite to a < b
a >= b	contextually convertible to bool	!(a < b)
a <= b	contextually convertible to bool	!(a > b)

The above rules imply that LegacyRandomAccessIterator also implements LessThanComparable.

A mutable LegacyRandomAccessIterator is a LegacyRandomAccessIterator that additionally satisfies the LegacyOutputIterator requirements.

Concept For the definition of std::iterator_traits, the following exposition-only concept is defined. template<class I> concept __LegacyRandomAccessIterator =   __LegacyBidirectionalIterator<I> && std::totally_ordered<I> &&   requires(I i, typename std::incrementable_traits<I>::difference_type n) {     { i += n } -> std::same_as<I&>;     { i -= n } -> std::same_as<I&>;     { i +  n } -> std::same_as<I>;     { n +  i } -> std::same_as<I>;     { i -  n } -> std::same_as<I>;     { i -  i } -> std::same_as<decltype(n)>;     {  i[n]  } -> std::convertible_to<std::iter_reference_t<I>>;   }; where the exposition-only concept __LegacyBidirectionalIterator is described in LegacyBidirectionalIterator#Concept.

(since C++20)

See also

random_access_iterator (C++20)	specifies that a bidirectional_iterator is a random-access iterator, supporting advancement in constant time and subscripting (concept)
Iterator library	provides definitions for iterators, iterator traits, adaptors, and utility functions