Array View¶

An array view is a light-weight container-like wrapper of a pointer and a size. It provides a convenient way to turn a contiguous memory region into a container-like object. In practice, such an object maintains the efficiency of a raw pointer while providing richer API to work with memory regions. Below is an example to illustrate this.

#include <clue/array_view.hpp>

using namespace clue;

int a[] = {1, 2, 3, 4, 5};

for (int& v: aview(a, 5)) {
    std::cout << v << std::endl;
    v += 1;
}

In practice, it is not uncommon that you maintain a vector in your object and would like to expose the elements to the users (without allowing the users to refer to the vector directly). In such cases, it would be a good idea to return an array view.

using namespace clue;

class A {
public:
    // ...

    array_view<const T> elements() const {
        return aview(elems_.data(), elems_.size());
    }

private:
    std::vector<T> elems_;
};

// client code

A a( /* ... */ );

std::cout << "# elems = " << a.elements().size() << std::endl;
for (const T& v: a.elements()) {
    std::cout << v << std::endl;
}

The `array_view` class template¶

class array_view¶

Formal:

template<typename T>
class array_view;

Parameters:	T – The element type.

Note

In general, array_view<T> allows modification of the elements, e.g a[i] = x. To provide a readonly view, one can use array_view<const T>.

Member types¶

The class array_view<T> contains a series of member typedefs as follows:

types	definitions
`value_type`	`std::remove_cv<T>::type`
`size_type`	`std::size_t`
`difference_type`	`std::ptrdiff_t`
`pointer`	`T*`
`const_pointer`	`const T*`
`reference`	`T&`
`const_reference`	`const T&`
`iterator`	implementing `RandomAccessIterator`
`const_iterator`	`iterator`
`reverse_iterator`	`std::reverse_iterator<iterator>`
`const_reverse_iterator`	`std::reverse_iterator<const_iterator>`

Construction¶

constexpr array_view() noexcept¶: Construct an empty view, with null data pointer.

constexpr array_view(pointer data, size_type len) noexcept¶: Construct an array view, with data pointer data and size len.

Note

It also has a copy constructor, an assignment operator, a destructor and a swap member function, all with default behaviors. It is worth noting that the copy construction/assignment of a view is shallow, meaning that only the pointer and the size value are copied, the underlying content remains there.

A convenient function aview is provided for constructing array views without the need of explicitly articulating the value type.

constexpr array_view<T> aview(T *p, size_t n) noexcept¶

Construct an array view, with data pointer p and size n.

Note:	If `p` is of type `T`, it returns a view of class `array_view<T>`, and if `p` is a const pointer of type `const T`, it returns a view of class `array_view<const T>`, which is a read-only view.

Basic properties and element access¶

constexpr size_type size() const noexcept¶: Get the size of the range, i.e. the number of elements referred to by the view.

constexpr bool empty() const noexcept¶: Get whether the view is empty, i.e. refers to no elements.

constexpr const_pointer data() const noexcept¶: Get a const pointer to the base address.

pointer data() noexcept¶: Get a pointer to the base address.

constexpr const_reference front() const¶: Get a const reference to the first element within the view.

reference front()¶: Get a reference to the first element within the view.

constexpr const_reference back() const¶: Get a const reference to the last element within the view.

reference back()¶: Get a reference to the last element within the view.

constexpr const_reference operator[](size_type pos) const¶: Get a const reference to the element at position pos, without bounds checking.

reference operator[](size_type pos)¶: Get a reference to the element at position pos, without bounds checking.

constexpr const_reference at(size_type pos) const¶

Get a const reference to the element at position pos, with bounds checking.

Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

reference at(size_type pos)¶

Get a reference to the element at position pos, with bounds checking.

Throw:	an exception of class `std::out_of_range` if `pos >= size()`.

Iterators¶

constexpr const_iterator cbegin() const¶: Get a const iterator to the beginning.

constexpr const_iterator cend() const¶: Get a const iterator to the end.

constexpr const_iterator begin() const¶: Get a const iterator to the beginning, equivalent to cbegin().

constexpr const_iterator end() const¶: Get a const iterator to the end, equivalent to cend().

iterator begin()¶: Get an iterator to the beginning.

iterator end()¶: Get an iterator to the end.

constexpr const_iterator crbegin() const¶: Get a const reverse iterator to the reversed beginning.

constexpr const_iterator crend() const¶: Get a const reverse iterator to the reversed end.

constexpr iterator rbegin() const¶: Get a const reverse iterator to the reversed beginning, equivalent to crbegin().

constexpr iterator rend() const¶: Get a const reverse iterator to the reversed end, equivalent to crend().

iterator rbegin()¶: Get a reverse iterator to the reversed beginning.

iterator rend()¶: Get a reverse iterator to the reversed end.