[range.access.rbegin]

# 25 Ranges library [[ranges]](./#ranges)

## 25.3 Range access [[range.access]](range.access#rbegin)

### 25.3.6 ranges​::​rbegin [range.access.rbegin]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L837)

The name ranges​::​rbegin denotes a customization point
object ([[customization.point.object]](customization.point.object "16.3.3.3.5 Customization Point Object types"))[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L841)

Given a subexpression E with type T,
let t be an lvalue that denotes the reified object for E[.](#2.sentence-1)

Then:

- [(2.1)](#2.1)

  If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges​::​rbegin(E) is ill-formed[.](#2.1.sentence-1)

- [(2.2)](#2.2)

  Otherwise, if T is an array type ([[dcl.array]](dcl.array#term.array.type "9.3.4.5 Arrays")) and remove_all_extents_t<T> is an incomplete type, ranges​::​rbegin(E) is ill-formed with no diagnostic required[.](#2.2.sentence-1)

- [(2.3)](#2.3)

  Otherwise, if auto(t.rbegin()) is a valid expression whose type models [input_or_output_iterator](iterator.concept.iterator#concept:input_or_output_iterator "24.3.4.6 Concept input_­or_­output_­iterator [iterator.concept.iterator]"), ranges​::​rbegin(E) is expression-equivalent to auto(t.rbegin())[.](#2.3.sentence-1)

- [(2.4)](#2.4)

  Otherwise, if T is a class or enumeration type and auto(rbegin(t)) is a valid expression whose type models [input_or_output_iterator](iterator.concept.iterator#concept:input_or_output_iterator "24.3.4.6 Concept input_­or_­output_­iterator [iterator.concept.iterator]") where the meaning of rbegin is established as-if by performing
 argument-dependent lookup only ([[basic.lookup.argdep]](basic.lookup.argdep "6.5.4 Argument-dependent name lookup")),
 then ranges​::​rbegin(E) is expression-equivalent to
 that expression[.](#2.4.sentence-1)

- [(2.5)](#2.5)

  Otherwise, if both ranges​::​begin(t) and ranges​::​end(t) are valid expressions of the same type which models [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") ([[iterator.concept.bidir]](iterator.concept.bidir "24.3.4.12 Concept bidirectional_­iterator")), ranges​::​rbegin(E) is expression-equivalent to make_reverse_iterator(ranges​::​end(t))[.](#2.5.sentence-1)

- [(2.6)](#2.6)

  Otherwise, ranges​::​rbegin(E) is ill-formed[.](#2.6.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L884)

[*Note [1](#note-1)*:

Diagnosable ill-formed cases above result in substitution failure
when ranges​::​rbegin(E) appears in the immediate context of a template instantiation[.](#3.sentence-1)

â *end note*]

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L891)

[*Note [2](#note-2)*:

Whenever ranges​::​rbegin(E) is a valid expression, its type models[input_or_output_iterator](iterator.concept.iterator#concept:input_or_output_iterator "24.3.4.6 Concept input_­or_­output_­iterator [iterator.concept.iterator]")[.](#4.sentence-1)

â *end note*]
