24 Containers library [containers]

24.6 Container adaptors [container.adaptors]

24.6.1 In general [container.adaptors.general]

The headers <queue>, <stack>, <flat_map>, and <flat_set> define the container adaptors queue and priority_queue, stack, flat_map and flat_multimap, and flat_set and flat_multiset, respectively.
Each container adaptor takes one or more template parameters named Container, KeyContainer, or MappedContainer that denote the types of containers that the container adaptor adapts.
Each container adaptor has at least one constructor that takes a reference argument to one or more such template parameters.
For each constructor reference argument to a container C, the constructor copies the container into the container adaptor.
If C takes an allocator, then a compatible allocator may be passed in to the adaptor's constructor.
Otherwise, normal copy or move construction is used for the container argument.
For the container adaptors that take a single container template parameter Container, the first template parameter T of the container adaptor shall denote the same type as Container​::​value_type.
For container adaptors, no swap function throws an exception unless that exception is thrown by the swap of the adaptor's Container, KeyContainer, MappedContainer, or Compare object (if any).
A constructor template of a container adaptor shall not participate in overload resolution if it has an InputIterator template parameter and a type that does not qualify as an input iterator is deduced for that parameter.
For container adaptors that have them, the insert, emplace, and erase members affect the validity of iterators, references, and pointers to the adaptor's container(s) in the same way that the containers' respective insert, emplace, and erase members do.
[Example 1:
A call to flat_map<Key, T>​::​insert can invalidate all iterators to the flat_map.
— end example]
A deduction guide for a container adaptor shall not participate in overload resolution if any of the following are true:
  • It has an InputIterator template parameter and a type that does not qualify as an input iterator is deduced for that parameter.
  • It has a Compare template parameter and a type that qualifies as an allocator is deduced for that parameter.
  • It has a Container, KeyContainer, or MappedContainer template parameter and a type that qualifies as an allocator is deduced for that parameter.
  • It has no Container, KeyContainer, or MappedContainer template parameter, and it has an Allocator template parameter, and a type that does not qualify as an allocator is deduced for that parameter.
  • It has both Container and Allocator template parameters, and uses_allocator_v<Container, Allocator> is false.
  • It has both KeyContainer and Allocator template parameters, and uses_allocator_v<KeyContainer, Allocator> is false.
  • It has both KeyContainer and Compare template parameters, and is_invocable_v<const Compare&, const typename KeyContainer::value_type&, const typename KeyContainer::value_type&> is not a valid expression or is false.
  • It has both MappedContainer and Allocator template parameters, and uses_allocator_v<MappedContainer, Allocator> is false.
The exposition-only alias template iter-value-type defined in [sequences.general] and the exposition-only alias templates iter-key-type, iter-mapped-type, range-key-type, and range-mapped-type defined in [associative.general] may appear in deduction guides for container adaptors.
The following exposition-only alias template may appear in deduction guides for container adaptors: template<class Allocator, class T> using alloc-rebind = // exposition only typename allocator_traits<Allocator>::template rebind_alloc<T>;