<< §4.4 Callin parameter mapping | ↑ Table of Contents ↑ | §4.6 Overriding access restrictions >> |
§4.5 Lifting and lowering
For basic definition see §2.2
and §2.3.
(The following rules are reverse forms of those from §3.3)
(a) Call target translation
Invoking a role method due to a callin binding first lifts the base object to the role class of the callin binding, in order to obtain the effective call target. This is why callin bindings cannot be defined in roles that are unliftable due to potential binding ambiguity (see §4.1.(b) above and §2.3.4.(a)).
(b) Parameter translation
During callin execution, each parameter for which the role method expects a role object is implicitly lifted to the declared role class.
(d) Typing rules
A parameter mapping (implicit by parameter position or explicit
by a with
clause) is well typed if
the right hand side conforms to the left hand side, either by
- type equality
- implicit primitive type conversion
- subtype polymorphism
- translation polymorphism, here: lifting;
however, withinreplace
bindings step 1 of the smart lifting algorithm (§2.3.3.(a)) is not applicable - or by a combination of the above.
A result mapping (implicit or explicit by a with
clause)
is well typed, if the value at the left hand conforms to the
right hand side according to the rules given above, except that
translation polymorphism here applies lowering instead of
lifting.
These rules define translation polymorphism as introduced in §2.3.
Additionally, in a replace
callin binding compatibility of parameters and return
types must hold in both directions.
Thus, from the above list of conversions a replace binding cannot apply subtype polymorphism
nor primitive type conversion.
If more flexibility is desired, type parameters can be used as defined in §4.10.
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