C++ named requirements: LegacyRandomAccessIterator

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

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

The type It satisfies LegacyRandomAccessIterator if

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	b - a > 0	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.

For the definition of std::iterator_traits, the following exposition-only concept is defined.

template<class I> concept __LegacyRandomAccessIterator = __LegacyBidirectionalIterator<I> && std::StrictTotallyOrdered<I> && requires(I i, typename std::incrementable_traits<I>::difference_type n) { { i += n } -> std::Same<I&>; { i -= n } -> std::Same<I&>; { i + n } -> std::Same<I>; { n + i } -> std::Same<I>; { i - n } -> std::Same<I>; { i - i } -> std::Same<decltype(n)>; { i[n] } -> std::iter_reference_t<I>; };

where the exposition-only concept __LegacyBidirectionalIterator is described in LegacyBidirectionalIterator#Concept.

(since C++20)

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