Java Reference
In-Depth Information
3. The type compliance of all parameters and evaluation of the when clause
takes place. If failure occurs, null is returned.
4. If the guard succeeds, the trace is consulted to see whether the mapping
has previously been satisfied for the given input. If so, the out parameters
are populated using the previous result and are returned. Otherwise, the
mapping body is entered.
5. The expressions found in the init section (if present) are executed in
sequence.
6. Following init , the “implicit instantiation” section is entered, where all
output objects are initialized, if still null . Collection types are initialized
with empty collections, and trace data is recorded for the mapping.
7. Each expression in the population section is executed in sequence, typi-
cally operating on the out or inout objects.
8. The end section expressions are then executed in sequence.
The execution semantics change when a mapping inherits, merges, or is a dis-
junction of another mapping, as described in Section 13.3.3, “Inheritance,
Merger, and Disjunction.”
return
During execution of a mapping operation or helper, you can control the flow
using explicit return statements. If a value is provided, it is assigned to the
result object of the mapping.
13.3.2 Entry Operation
A special form of mapping, known as the entry operation, is marked with the
main keyword. There can be only one main per transformation—or, in the case
of abstract transformations, no main operation at all. If used without mapping ,
this entry point takes no parameters and has no init , population , or end
block. A main can be used with the mapping keyword and combines the aspects
of the transformation entry point and those of a regular mapping operation.
Following is a main that does not declare that it's a mapping operation. The out-
put is assigned the result of the toRequirementsModel() mapping. As you can
see, QVTO allows parameters in main operations, although it's technically not
allowed in the specification.
Search WWH ::




Custom Search