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Papyrus/Designer/code-generation

Code generation

The result of the previous phase is a component model of the application, enriched with reified connectors and expanded containers. The code generation starting from this model requires two actions: (1) the realization of the component deployment consisting of a splitting the global model into sub models for each execution node and (2) the transformation of ports and connectors that do not have a direct equivalent concepts in object-oriented programming languages.

The former is not as trivial as it may seem since dependencies have to be taken into account and composites may have to be deployed on multiple nodes due to allocations of theirs parts. This imposes constraints such as only read-only attributes in these composites to ensure consistency. We do not discuss this issue further in the context of this paper and focus on the second aspect, the transformation of ports and connectors.

Ports and connectors do not possess a direct equivalent in an object-oriented programming language. Thus, it is necessary to relate component-oriented concepts to object-oriented concepts, i.e. classes, interfaces, attributes and operations. We distinguish ports with provided interfaces and ports with required interfaces (a port might also have both). A port providing an interface is an access point to a service and a caller needs to obtain a reference to this service, in our implementation pattern via a specific operation. For instance, if a component owns a port "p" providing interface "I", the realization of a component needs an operation "get_p" returning a reference to the service. The implementation of this operation is determined automatically: in case of a delegation connector between the port and an internal part of a component, this reference is returned, otherwise a reference to the component reference itself is returned.

A port with a required interface is an interaction point which requires a reference of another component that provides the interface. Thus, the component needs to store this reference and provide an operation to initialize the reference in the moment of instantiation. For instance, a port "q" with an required interface is transformed into an attribute which stores a reference to a port providing the interface and an operation "connect_q" which initializes this reference.

Connectors within a composite are transformed into a realization of a specific operation that creates the connections between parts, i.e. contains suitable combinations of some-part.connect_some-port other-part.get_other-port.

Once the transformation of component-based models to object-oriented models is done, a "classical" code generator taking an object-oriented UML model as input is sufficient for the code generation (in our case C++). For each class or interface, a C++ class is generated. The UML packages are transformed into C++ name spaces. The organization of the files follows the same as in Java. A name space corresponds to a directory and thus reflects the package structure in UML.

The dependencies to the external packages are translated into include directives to libraries. The generated code can now be compiled, for instance in the context of the Eclipse CDT environment.

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