View Template Library

transform_view<Container, Transform, Const_tag, T, Base>


Category: adaptors	Component type: type

Description

The transform_view template represents objects that reference one container, and that have methods for accessing its elements. The properties of any transform_view instance depend on the properties of the container template parameter. The interface of transform_view adapts itself [1] to the referenced container, if this is one of Container provides a Container interface, a transform_view referencing Forward Containers provides a Forward Container interface while a Random Access Container provides a Random Access Conatiner interface, or Sequence interface.

The transform_view presents transformed values, depending on the transformation template parameter. Transformation is only applied in presenting the elements, the container's elements themselves are not altered.

The properties of the order of elements are the same as those provided by the underlying container, as is the validity of more than one active iterators at any one time.

A transform_view owns its referenced container, if its base template parameter is aggregated_ownership, it merely references its container, if the base template parameter is referenced_ownership.

Template parameters

Parameter	Description	Default
`container`	The view's container type: the type of container referenced by this view
`transformation`	The view's transformation type: the type of the transformation used to transform the container's elements
`const_tag`	The view's const tag: either `const_view_tag` or `mutable_view_tag`	`const_view_tag`
`T`	The view's value type: the type of elements referenced by this view.	`transformation::result_type`
`base`	The view's ownership type: the base class that determines if the view references or owns the container	`referenced_ownership`

Definition

Defined in the header transform_view.hpp.

Model of

View

Type requirements

T has to be assignable. transformation has to be a functor with result type T and argument type container::value_type. transformation's operator() has to be a const member.

Members

Member	Where defined	Description
`value_type`	Container	The type `T` of the elements accessed through the container.
`domain_t`	view	The type of the referenced container.
`transform_t`	view	The type of the transformation.
`pointer`	Container	Pointer to `T`.
`reference`	Container	`T`
`const_reference`	Container	`const T`
`size_type`	Container	An unsigned integral type.
`difference_type`	Container	A signed integral type.
`iterator`	Container	Iterator used to iterate through the view.
`const_iterator`	Container	Const iterator used to iterate through the view.
`reverse_iterator`	Reversible Container	Iterator used to iterate backwards through the view.
`const_reverse_iterator`	Reversible Container	Const iterator used to iterate backwards through the view.
`iterator begin()`	Container	Returns an iterator pointing to the begin of the view.
`iterator end()`	Container	Returns an iterator pointing to the end of the view.
`const_iterator begin() const`	Container	Returns a const_iterator pointing to the begin of the view.
`const_iterator end() const`	Container	Returns a const_iterator pointing to the end of the view.
`reverse_iterator rbegin()`	Reversible Container	Valid for reversible container's only. Returns a `reverse_iterator` pointing to the beginning of the reversed view.
`reverse_iterator rend()`	Reversible Container	Valid for reversible container's only. Returns a `reverse_iterator` pointing to the end of the reversed view.
`const_reverse_iterator rbegin() const`	Reversible Container	Valid for reversible container's only. Returns a `const_reverse_iterator` pointing to the beginning of the reversed view.
`const_reverse_iterator rend() const`	Reversible Container	Valid for reversible container's only. Returns a `const_reverse_iterator` pointing to the end of the reversed view.
`reference front()`	Sequence	Returns a `reference` for the first element in the view. Only supported if container is a sequence.
`reference back()`	Sequence	Returns a `reference` for the last element in the view. Only supported if container is a sequence.
`const_reference front() const`	Sequence	Returns a `const_reference` for the first element in the view. Only supported if container is a sequence.
`const_reference back() const`	Sequence	Returns a `const_reference` for the last element in the view. Only supported if container is a sequence.
`void pop_front()`	Sequence	Call pop_front on the underlying container.
`void pop_back()`	Sequence	Call pop_back on the underlying container.
`reference operator[](size_type n)`	Random access container	Returns a `reference` for the nth element in the view. Only supported if container is random access.
`const_reference operator[](size_type n) const`	Random access container	Returns a `const_reference` for the nth element in the view. Only supported if container is random access.
`reference at(size_type n)`	Random access container	Returns a `reference` for the nth element in the view. Only supported if container is random access. Does a range check on n and will throw `std::range_error` if it fails.
`const_reference at(size_type n) const`	Random access container	Returns a `const_reference` for the nth element in the view. Only supported if container is random access. Does a range check on n and will throw `std::range_error` if it fails.
`size_type size() const`	Container	Returns the size of the view.
`size_type max_size() const`	Container	Returns the largest possible size of the view.
`bool empty() const`	Container	true if the view's size is 0.
`transform_view()`	view	Creates an empty view.
`transform_view(container_t&, const transform_t&)`	view	Creates a view of given container.
`void swap(transform_view&)`	Container	Swaps the two views. Iterators are invalidated by this operation. For referencing views, the containers themselves are not swapped.
`bool operator==(const transform_view&, const transform_view&)`	Forward Container	Tests two views for equality. This is a global function, not a member function. Views may be equal even if their referenced containers are not.
`bool operator<(const transform_view&, const transform_view&)`	Forward Container	Lexicographical comparison. This is a global function, not a member function.

Notes

[1] Since in general the transformation results in temporary objects, non const references as return value of e.g. front are useless. Instead, reference is defined to be the same as value_type here. Whether and how altering the elements of the view affects the elements of the referenced contianer depends on the template parameter const_tag and the transformation.