# C++ standard libraries extensions

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< cpp‎ | experimental

The C++ Extensions for Library Fundamentals, ISO/IEC TS 19568:2015 defines the following new components for the C++ standard library:

# Not merged into C++17

The following components of ISO/IEC TS 19568:2015 were not selected for inclusion in C++17

#### Modified versions of existing classes to support type-erased allocators

Defined in header `<experimental/functional>`
function | a modified version of std::function with support for type-erased allocators (class template)
Defined in header `<experimental/future>`
promise | a modified version of std::promise with support for type-erased allocators (class template)
packaged_task | a modified version of std::packaged_task with support for type-erased allocators (class template)

#### Polymorphic allocators and memory resources

resource_adaptor | adapts an allocator into a memory_resource (alias template)

### General utilities

Defined in header `<experimental/utility>`
erased_type | placeholder type for type erasure, such as in allocators (class)
Defined in header `<experimental/type_traits>`
invocation_type raw_invocation_type | deduce the implied function type of the callable object when called with the given argument types (class template)

# Merged into C++17

The following components of ISO/IEC TS 19568:2015 were included into C++17

### optional objects

Defined in header `<experimental/optional>`
optional | a class template representing optional objects (class template)

### class `any`

Defined in header `<experimental/any>`
any | a type-safe container for single values of any type (class)

### `string_view`

Defined in header `<experimental/string_view>`
basic_string_view | a non-owning reference to a string (class template)

### Type-erased and polymorphic allocators

#### Polymorphic allocators and memory resources

The entities in this section are declared in the std::experimental::pmr namespace.

Defined in header `<experimental/memory_resource>`
memory_resource | an abstract interface for classes that encapsulate memory resources (class)
synchronized_pool_resource | a thread-safe memory_resource for managing allocations in pools of different block sizes (class)
unsynchronized_pool_resource | a thread-unsafe memory_resource for managing allocations in pools of different block sizes (class)
monotonic_buffer_resource | a special-purpose memory_resource that releases the allocated memory only when the resource is destroyed (class)
polymorphic_allocator | an allocator that supports run-time polymorphism based on the memory_resource it is constructed with (class template)
new_delete_resource | returns a static program-wide `memory_resource` that uses the global operator new and operator delete to allocate and deallocate memory (function)
null_memory_resource | returns a static `memory_resource` that performs no allocation (function)
get_default_resource | gets the default `memory_resource` (function)
set_default_resource | sets the default `memory_resource` (function)

#### Convenience aliases for containers using polymorphic allocators

Convenience aliases and alias templates for containers using polymorphic allocators are provided in the `std::experimental::pmr` namespace for the following class templates in the standard library:

List of container templates for which convenience aliases are provided

- std::vector
- std::deque
- std::forward_list
- std::list
- std::basic_string
- std::map
- std::multimap
- std::set
- std::multiset
- std::match_results
- std::unordered_map
- std::unordered_multimap
- std::unordered_set
- std::unordered_multiset

### Array support for `shared_ptr`

Defined in header `<experimental/memory>`
Class | Description
shared_ptr | A modified version of std::shared_ptr that supports arrays (class template)
weak_ptr | A modified version of std::weak_ptr that supports arrays (class template)

### Sampling and searching algorithms

Defined in header `<experimental/algorithm>`
sample | selects n random elements from a sequence (function template)
search | applies a Searcher to a sequence (function template)
Defined in header `<experimental/functional>`
default_searcher | standard C++ library search algorithm implementation (class template)
make_default_searcher | helper function to create a default_searcher (function template)
boyer_moore_searcher | Boyer-Moore search algorithm implementation (class template)
make_boyer_moore_searcher | helper function to create a boyer_moore_searcher (function template)
boyer_moore_horspool_searcher | Boyer-Moore-Horspool search algorithm implementation (class template)
make_boyer_moore_horspool_searcher | helper function to create a boyer_moore_horspool_searcher (function template)

### General utilities

Defined in header `<experimental/tuple>`
apply | calls a function to a tuple of arguments (function template)

In addition, the TS provides numerous `constexpr` variable templates for the following type traits and other class templates in the standard library:

List of type traits and other class templates for which variable templates are provided

- std::is_void
- std::is_null_pointer
- std::is_integral
- std::is_floating_point
- std::is_array
- std::is_pointer
- std::is_lvalue_reference
- std::is_rvalue_reference
- std::is_member_object_pointer
- std::is_member_function_pointer
- std::is_enum
- std::is_union
- std::is_class
- std::is_function
- std::is_reference
- std::is_arithmetic
- std::is_fundamental
- std::is_object
- std::is_scalar
- std::is_compound
- std::is_member_pointer
- std::is_const
- std::is_volatile
- std::is_trivial
- std::is_trivially_copyable
- std::is_standard_layout
- std::is_pod
- std::is_literal_type
- std::is_empty
- std::is_polymorphic
- std::is_abstract
- std::is_final
- std::is_signed
- std::is_unsigned
- std::is_constructible
- std::is_trivially_constructible
- std::is_nothrow_constructible
- std::is_default_constructible
- std::is_trivially_default_constructible
- std::is_nothrow_default_constructible
- std::is_copy_constructible
- std::is_trivially_copy_constructible
- std::is_nothrow_copy_constructible
- std::is_move_constructible
- std::is_trivially_move_constructible
- std::is_nothrow_move_constructible
- std::is_assignable
- std::is_trivially_assignable
- std::is_nothrow_assignable
- std::is_copy_assignable
- std::is_trivially_copy_assignable
- std::is_nothrow_copy_assignable
- std::is_move_assignable
- std::is_trivially_move_assignable
- std::is_nothrow_move_assignable
- std::is_destructible
- std::is_trivially_destructible
- std::is_nothrow_destructible
- std::has_virtual_destructor
- std::alignment_of
- std::rank
- std::extent
- std::is_same
- std::is_base_of
- std::is_convertible
- std::ratio_equal
- std::ratio_not_equal
- std::ratio_less
- std::ratio_less_equal
- std::ratio_greater
- std::ratio_greater_equal
- std::tuple_size
- std::chrono::treat_as_floating_point
- std::is_error_code_enum
- std::is_error_condition_enum
- std::is_bind_expression
- std::is_placeholder
- std::uses_allocator

### Feature test macros

Defined in header `<experimental/optional>`
__cpp_lib_experimental_optional | a value of at least 201411 indicates that the optional type is supported (macro constant)
Defined in header `<experimental/any>`
__cpp_lib_experimental_any | a value of at least 201411 indicates that the any type is supported (macro constant)
Defined in header `<experimental/string_view>`
__cpp_lib_experimental_string_view | a value of at least 201411 indicates that basic_string_view template is supported (macro constant)
Defined in header `<experimental/tuple>`
__cpp_lib_experimental_apply | a value of at least 201402 indicates that the tuple apply() function is supported (macro constant)
Defined in header `<experimental/type_traits>`
__cpp_lib_experimental_type_trait_variable_templates | a value of at least 201402 indicates that variable template type traits are supported (macro constant)
__cpp_lib_experimental_invocation_type | a value of at least 201406 indicates that invocation type traits are supported (macro constant)
Defined in header `<experimental/functional>`
__cpp_lib_experimental_boyer_moore_searching | a value of at least 201411 indicates that additional searching algorithms are supported (macro constant)
__cpp_lib_experimental_function_erased_allocator | a value of at least 201406 indicates that type-erased allocator for std::function is supported (macro constant)
Defined in header `<experimental/future>`
__cpp_lib_experimental_promise_erased_allocator | a value of at least 201406 indicates that type-erased allocator for std::promise is supported (macro constant)
__cpp_lib_experimental_packaged_task_erased_allocator | a value of at least 201406 indicates that type-erased allocator for std::packaged_task is supported (macro constant)
Defined in header `<experimental/memory>`
__cpp_lib_experimental_shared_ptr_arrays | a value of at least 201406 indicates that shared_ptr arrays are supported (macro constant)
Defined in header `<experimental/memory_resource>`
__cpp_lib_experimental_memory_resources | a value of at least 201402 indicates that polymorphic memory resources are supported (macro constant)
Defined in header `<experimental/algorithm>`
__cpp_lib_experimental_sample | a value of 201402 indicates that the sample algorithm is supported (macro constant)

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