[range.prim.size]

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

## 25.3 Range access [[range.access]](range.access#range.prim.size)

### 25.3.10 ranges​::​size [range.prim.size]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L1024)

The name ranges​::​size 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#L1028)

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 T is an array of unknown bound ([[dcl.array]](dcl.array#term.array.type "9.3.4.5 Arrays")), ranges​::​size(E) is ill-formed[.](#2.1.sentence-1)

- [(2.2)](#2.2)

  Otherwise, if T is an array type, ranges​::​size(E) is expression-equivalent to auto(extent_v<T>)[.](#2.2.sentence-1)

- [(2.3)](#2.3)

  Otherwise, if disable_sized_range<remove_cv_t<T>> ([[range.sized]](range.sized "25.4.4 Sized ranges"))
 is false and auto(t.size()) is a valid expression of integer-like type ([[iterator.concept.winc]](iterator.concept.winc "24.3.4.4 Concept weakly_­incrementable")), ranges​::​size(E) is expression-equivalent to auto(​t.size())[.](#2.3.sentence-1)

- [(2.4)](#2.4)

  Otherwise, if T is a class or enumeration type, disable_sized_range<remove_cv_t<T>> is false and auto(size(t)) is a valid expression of integer-like type
 where the meaning of size 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​::​size(E) is expression-equivalent to
 that expression[.](#2.4.sentence-1)

- [(2.5)](#2.5)

  Otherwise, if *to-unsigned-like*(ranges​::​end(t) - ranges​::​begin(t)) ([[ranges.syn]](ranges.syn "25.2 Header <ranges> synopsis"))
 is a valid expression and
 the types I and S of ranges​::​begin(t) and ranges​::​end(t) (respectively) model both [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<S, I> ([[iterator.concept.sizedsentinel]](iterator.concept.sizedsentinel "24.3.4.8 Concept sized_­sentinel_­for")) and [forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")<I>,
 then ranges​::​size(E) is expression-equivalent to *to-unsigned-like*(ranges​::​end(t) - ranges​::​begin(t))[.](#2.5.sentence-1)

- [(2.6)](#2.6)

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

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L1075)

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

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

— *end note*]

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L1082)

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

Whenever ranges​::​size(E) is a valid expression, its
type is integer-like[.](#4.sentence-1)

— *end note*]