# Operations¶

An operation is a function that transforms a descriptor and other arguments represented via an input object to a result object. An operation is responsible for:

• Executing all of an algorithm’s computational routines represented by the descriptor.

• Passing SYCL* queue to computational routines.

• Verifying preconditions and postconditions before and after the execution of computational routines.

## General operation definition¶

The following code sample shows the declaration of an abstract operation. To declare a particular operation, the %OPERATION% shall be substituted with the name of the operation.

namespace oneapi::dal {

template <typename Descriptor>
using %OPERATION%_input_t = /* implementation defined */;

template <typename Descriptor>
using %OPERATION%_result_t = /* implementation defined */;

template <typename Descriptor>
%OPERATION%_result_t<Descriptor> %OPERATION%(
sycl::queue& queue,
const Descriptor& desc,
const %OPERATION%_input_t<Descriptor>& input);

} // namespace oneapi::dal


Each operation shall satisfy the following requirements:

• An operation shall accept three parameters in the following order:

• The SYCL* queue object

• The descriptor of the algorithm

• The input object

• An operation shall return the result object.

• The %OPERATION%_input_t and %OPERATION%_result_t alias templates shall be used for inference of the input and return types.

• If a precondition is violated, an operation shall throw an exception derived from oneapi::dal::logic_error.

• If a postcondition is violated, an operation shall throw an exception derived from oneapi::dal::runtime_error.

• If the descriptor is incompatible with some operation, an error shall be reported at compile-time.

• The exact list of compatible operations and pre-/post- conditions shall be defined by a particular algorithm specification.

## Operation shortcuts¶

In order to make the code on user side less verbose, oneDAL defines the following overloaded functions called shortcuts for each operation in addition to the general one described in section General operation definition.

• A shortcut for execution on host that performs the same operation as the general function on host, but does not require the queue to be passed explicitly.

template <typename Descriptor>
%OPERATION%_result_t<Descriptor> %OPERATION%(
const Descriptor& desc,
const %OPERATION%_input_t<Descriptor>& input);

• A shortcut that allows omitting explicit input creation.

template <typename Descriptor, typename... Args>
%OPERATION%_result_t<Descriptor> %OPERATION%(
sycl::queue& queue,
const Descriptor& desc,
Args&&... args);

• A shortcut that allows omitting explicit queue and input creation. This is a combination of two previous shortcuts.

template <typename Descriptor, typename... Args>
%OPERATION%_result_t<Descriptor> %OPERATION%(
const Descriptor& desc,
Args&&... args);


## Input¶

An input object aggregates all the data that the algorithm requires for performing a specific operation. The data is represented via tables, so, typically, an input is a collection of tables, but not limited to them and can aggregate objects of an arbitrary type.

In general, input class definition is similar to descriptor. An input defines properties that can be accessed by means of the corresponding getter and setter methods. Requirements to the input’s properties are the same as requirements for descriptor’s properties.

The following code sample shows the common structure of a inputs’s definition. To define an input for particular algorithm and operation, the following strings shall be substituted:

• %ALGORITHM% is the name of an algorithm and its namespace.

• %OPERATION% is the name of operation.

• %PROPERTY_NAME% and %PROPERTY_TYPE% are the name and the type of one of the input’s properties.

namespace oneapi::dal::%ALGORITHM% {

class OPERATION_input {
public:
/* Constructor */
%OPERATION%_input(const %PROPERTY_TYPE%& %PROPERTY_NAME%,
/* more properties */)

/* Getter & Setter for the property called %PROPERTY_NAME% */
descriptor& set_%PROPERTY_NAME%(%PROPERTY_TYPE% value);
%PROPERTY_TYPE% get_%PROPERTY_NAME%() const;

/* more properties */
};

} // namespace oneapi::dal::%ALGORITHM%


Note

An input is specific to algorithm and operation, so each %ALGORITHM%-%OPERATION% pair shall define its own set of the properties.

## Result¶

A result object aggregates all output values computed by the algorithm. All assumptions about an input are applied to a result as well.

namespace oneapi::dal::%ALGORITHM% {

class OPERATION_result {
public:
/* Constructor */
%OPERATION%_result(const %PROPERTY_TYPE%& %PROPERTY_NAME%,
/* more properties */)

/* Getter & Setter for the property called %PROPERTY_NAME% */
descriptor& set_%PROPERTY_NAME%(%PROPERTY_TYPE% value);
%PROPERTY_TYPE% get_%PROPERTY_NAME%() const;

/* more properties */
};

} // namespace oneapi::dal::%ALGORITHM%