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Re: [mdt-ocl.dev] retyping through oclAsType; clarifications
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And I forgot part of the question ...
We're told that "If the actual type of the object, at evaluation time,
is not a subtype of the type to which it is re-typed, then the result
of oclAsType is invalid.". Yet A.2.6 tells us "OclVoid is the subtype of
all other types." which would mean C is not invalid ... but what would
be the result?
Laurent Goubet a écrit :
Hi all,
I need some clarifications about the actual definition of the
"oclAsType" operation. I'll refer to some parts of the specification
here and there; I'm refering to the 2.1 draft for this.
here are the four examples I'll base my ramblings on :
A- 3.oclAsType(Integer)
B- 3.oclAsType(Real)
C- 3.oclAsType(OclVoid)
D- 3.oclAsType(OclInvalid)
And the actual question : what are the expected results of each of
these? I would say
A- integer "3"
B- integer "3"
C- invalid
D- invalid
Why I am confused about these?
7.4.6 tells us :
----------8<----------
object.oclAsType(Type2) --- changes the static type of the
expression to Type2
An object can only be re-typed to a type to which it conforms. If the
actual type of the object, at evaluation time, is not
a subtype of the type to which it is re-typed, then the result of
oclAsType is invalid.
Casting provides visibility, at parse time, of features not defined in
the context of an expression's static type. It does not
coerce objects to instances of another type, nor can it provide access
to hidden or overridden features of a type. For this,
the feature call is qualified by the name of the type (a path name, if
necessary) whose definition of the feature is to be
accessed.
---------->8----------
Which confirms the "expected results" I gave above. Yet
7.5.9 lists :
----------8<----------
oclAsType (t : OclTypeClassifier) : instance of OclType
---------->8----------
so the result of B should be the "double" 3.0 and not the "integer" 3.
11.2.5 seems to confirm this with the post condition of oclAsType :
----------8<----------
post: (result = self) and result.oclIsTypeOf( t )
---------->8----------
Except if "oclIsTypeOf" checks the static type of its source instead
of its actual type.
I believe that both 7.5.9 and 11.2.5 should be revisited to take into
account the rules of 7.4.6 that were updated with OCL 2.1.
Furthermore, 7.4.6 tells us that "If the actual type of the object, at
evaluation time, is not a subtype of the type to which it is re-typed,
then the result of oclAsType is invalid." whereas 11.2.5 says "if the
actual type of self at evaluation time does not conform to t, then the
oclAsType operation evaluates to null." which makes unclear the
results of both C and D above.
What do you think about these?
Laurent
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