## §3.3 Lifting and lowering

(For basic definitions see §2.2 and §2.3)

#### (a) Call target translation

Invoking a base method due to a callout binding first lowers the role object in order to obtain the effective call target.

#### (b) Parameter translation

Passing a role object as parameter to a callout method implicitly lowers this parameter, if the base method declares a corresponding base type parameter.
Lifting of callout parameters is not possible.

#### (c) Result translation

When returning a base object from a callout method where the role method declares the result to be of a role class, this object is implicitly lifted to the appropriate role.
Lowering the result of a callout binding is not possible.

#### (d) Typing rules

A parameter mapping (implicit by parameter position or explicit by a `with` clause) is well typed if the left hand side conforms to the right hand side, either by

- type equality
- implicit primitive type conversion
- subtype polymorphism
- translation polymorphism, here: lowering,
- 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 right hand side conforms to the left hand side according to the rules given above, except that translation polymorphism here applies lifting instead of lowering.

#### (e) Role arrays

For arrays of roles as parameters §2.2.(e) applies accordingly. For arrays as a return value §2.3.(d) applies.