[indirect.hash]

# 20 Memory management library [[mem]](./#mem)

## 20.4 Types for composite class design [[mem.composite.types]](mem.composite.types#indirect.hash)

### 20.4.1 Class template indirect [[indirect]](indirect#hash)

#### 20.4.1.10 Hash support [indirect.hash]

[🔗](#lib:hash,indirect)

`template<class T, class Allocator>
struct hash<indirect<T, Allocator>>;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L6740)

The specialization hash<indirect<T, Allocator>> is enabled ([[unord.hash]](unord.hash "22.10.19 Class template hash")) if and only if hash<T> is enabled[.](#1.sentence-1)

When enabled for an object i of type indirect<T, Allocator>,hash<indirect<T, Allocator>>()(i) evaluates to
either the same value as hash<T>()(*i),
if i is not valueless;
otherwise to animplementation-defined
value[.](#1.sentence-2)

The member functions are not guaranteed to be noexcept[.](#1.sentence-3)