# xoptional_assembly_base¶

Defined in xtensor/xoptional_assembly_base.hpp

template <class D>
class xoptional_assembly_base : xt::xiterable<D>

Base class for dense multidimensional optional assemblies.

The xoptional_assembly_base class defines the interface for dense multidimensional optional assembly classes. Optional assembly classes hold optional values and are optimized for tensor operations. xoptional_assembly_base does not embed any data container, this responsibility is delegated to the inheriting classes.

Template Parameters
• D: The derived type, i.e. the inheriting class for which xoptional_assembly_base provides the interface.

Size and shape

auto size() const

Returns the number of element in the optional assembly.

auto constexpr dimension() const

Returns the number of dimensions of the optional assembly.

auto shape() const

Returns the shape of the optional assembly.

auto strides() const

Returns the strides of the optional assembly.

auto backstrides() const

Returns the backstrides of the optional assembly.

Data

template <class... Args>
auto operator()(Args... args)

Returns a reference to the element at the specified position in the optional assembly.

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the optional assembly.

template <class... Args>
auto operator()(Args... args) const

Returns a constant reference to the element at the specified position in the optional assembly.

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the optional assembly.

template <class... Args>
auto at(Args... args)

Returns a reference to the element at the specified position in the optional assembly, after dimension and bounds checking.

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices should be equal to the number of dimensions of the optional assembly.
Exceptions
• std::out_of_range: if the number of argument is greater than the number of dimensions or if indices are out of bounds.

template <class... Args>
auto at(Args... args) const

Returns a constant reference to the element at the specified position in the optional assembly, after dimension and bounds checking.

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices should be equal to the number of dimensions of the optional assembly.
Exceptions
• std::out_of_range: if the number of argument is greater than the number of dimensions or if indices are out of bounds.

template <class... Args>
auto unchecked(Args... args)

Returns a reference to the element at the specified position in the optional assembly.

Warning
This method is meant for performance, for expressions with a dynamic number of dimensions (i.e. not known at compile time). Since it may have undefined behavior (see parameters), operator() should be prefered whenever it is possible.
Warning
This method is NOT compatible with broadcasting, meaning the following code has undefined behavior:
xt::xarray<double> a = {{0, 1}, {2, 3}};
xt::xarray<double> b = {0, 1};
auto fd = a + b;
double res = fd.uncheked(0, 1);

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the optional assembly, else the behavior is undefined.

template <class... Args>
auto unchecked(Args... args) const

Returns a constant reference to the element at the specified position in the optional assembly.

Warning
This method is meant for performance, for expressions with a dynamic number of dimensions (i.e. not known at compile time). Since it may have undefined behavior (see parameters), operator() should be prefered whenever it is possible.
Warning
This method is NOT compatible with broadcasting, meaning the following code has undefined behavior:
xt::xarray<double> a = {{0, 1}, {2, 3}};
xt::xarray<double> b = {0, 1};
auto fd = a + b;
double res = fd.uncheked(0, 1);

Parameters
• args: a list of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the optional assembly, else the behavior is undefined.

template <class S>
auto operator[](const S &index)

Returns a reference to the element at the specified position in the optional assembly.

Parameters
• index: a sequence of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices in the list should be equal or greater than the number of dimensions of the optional assembly.

template <class S>
auto operator[](const S &index) const

Returns a constant reference to the element at the specified position in the optional assembly.

Parameters
• index: a sequence of indices specifying the position in the optional assembly. Indices must be unsigned integers, the number of indices in the list should be equal or greater than the number of dimensions of the optional assembly.

template <class It>
auto element(It first, It last)

Returns a reference to the element at the specified position in the optional assembly.

Parameters
• first: iterator starting the sequence of indices
• last: iterator ending the sequence of indices The number of indices in the sequence should be equal to or greater than the number of dimensions of the optional assembly.

template <class It>
auto element(It first, It last) const

Returns a constant reference to the element at the specified position in the optional assembly.

Parameters
• first: iterator starting the sequence of indices
• last: iterator ending the sequence of indices The number of indices in the sequence should be equal to or greater than the number of dimensions of the optional assembly.

template <class S>
bool broadcast_shape(S &shape, bool reuse_cache = false) const

Broadcast the shape of the optional assembly to the specified parameter.

Return
a boolean indicating whether the broadcasting is trivial
Parameters
• shape: the result shape
• reuse_cache: parameter for internal optimization

template <class S>
bool has_linear_assign(const S &strides) const

Checks whether the xoptional_assembly_base can be linearly assigned to an expression with the specified strides.

Return
a boolean indicating whether a linear assign is possible

Public Functions

template <class S = shape_type>
void resize(const S &shape, bool force = false)

Resizes the optional assembly.

Parameters
• shape: the new shape
• force: force reshaping, even if the shape stays the same (default: false)

template <class S = shape_type>
void resize(const S &shape, layout_type l)

Resizes the optional assembly.

Parameters
• shape: the new shape
• l: the new layout_type

template <class S = shape_type>
void resize(const S &shape, const strides_type &strides)

Resizes the optional assembly.

Parameters
• shape: the new shape
• strides: the new strides

template <class S = shape_type>
void reshape(const S &shape, layout_type layout = static_layout)

Reshapes the optional assembly.

Parameters
• shape: the new shape
• layout: the new layout

layout_type layout() const

Return the layout_type of the container.

Return
layout_type of the container

template <class T>
void fill(const T &value)

Fills the data with the given value.

Parameters
• value: the value to fill the data with.

auto value()

Return an expression for the values of the optional assembly.

auto value() const

Return a constant expression for the values of the optional assembly.

auto has_value()

Return an expression for the missing mask of the optional assembly.

auto has_value() const

Return a constant expression for the missing mask of the optional assembly.