[random.access.iterators] (original) (raw)
A class or pointer typeXmeets the requirements of a random access iterator if, in addition to meeting the Cpp17BidirectionalIterator requirements, the following expressions are valid as shown in Table 81.
Table 81 — Cpp17RandomAccessIterator requirements (in addition to Cpp17BidirectionalIterator) [tab:randomaccessiterator]
| 🔗Expression | Return type | Operational | Assertion/note |
|---|---|---|---|
| 🔗 | semantics | pre-/post-condition | |
| 🔗r += n | X& | { difference_type m = n; if (m >= 0) while (m--) ++r; else while (m++) --r; return r; } | |
| 🔗a + nn + a | X | { X tmp = a; return tmp += n; } | a + n == n + a. |
| 🔗r -= n | X& | return r += -n; | Preconditions: the absolute value of n is in the range of representable values of difference_type. |
| 🔗a - n | X | { X tmp = a; return tmp -= n; } | |
| 🔗b - a | difference_type | return n; | Preconditions: there exists a value n of type difference_type such that a + n == b. b == a + (b - a). |
| 🔗a[n] | convertible to reference | *(a + n) | |
| 🔗a < b | decltype(a < b) models boolean-testable | Effects: Equivalent to: return b - a > 0; | < is a total ordering relation |
| 🔗a > b | decltype(a > b) models boolean-testable | b < a | > is a total ordering relation opposite to <. |
| 🔗a >= b | decltype(a >= b) models boolean-testable | !(a < b) | |
| 🔗a <= b | decltype(a <= b) models boolean-testable | !(a > b) |