ADA13 — narrowing of valuetypes

Paragraph 5.2.6 of CORBA v2.3.1 specifies that "value type
instances may be widened/narrowed to other value types. Each language
mapping is responsible for specifying how these operations are made
available to the programmer." Ada mapping v1.2 specifies a
To_Abstract_Value function to widen a value type to an abstract value
type (paragraph 1.10.2.2). The same document reads that concrete value
types may be widened to other concrete value types using ada's view
conversion (paragraph 1.10.2.3). However, nothing is specified to
support narrowing of value types (concrete or abstract) to inheriting
concrete value types.

Proposed solution: We propose the definition of a To_Value_Ref function
in the helper package associated with the value type, with the following
signature:
function To_Value_Ref
(From : in CORBA.Value.Base'Class)
return Value_Ref;

The semantic of this function would be to cast the object reference
passed as a paramater to a reference of the current interface, if it
is legal. Otherwise, this function would raise CORBA.Bad_Param.

Proposed solution:
We propose the definition of a To_Value_Ref function in the helper package
associated with the value type, with the following signature:
function To_Value_Ref
(From : in CORBA.Value.Base'Class)
return Value_Ref;
The semantic of this function would be to cast the object reference passed as a
parameter to a reference of the current interface, if it is legal. Otherwise, this
function would raise CORBA.Bad_Param.
Resolution:
Accept as suggested.