13.6 Change of Representation
A
type_conversion
(see
4.6) can be used to convert between two
different representations of the same array or record. To convert an
array from one representation to another, two array types with matching
component subtypes and convertible index types are required. If one type
has Pack specified and the other does not, then explicit conversion can
be used to pack or unpack an array.
To convert an untagged record from one representation
to another, two record types with a common ancestor type are required.
Distinct representations can then be specified for the record types,
and explicit conversion between the types can be used to effect a change
in representation.
Examples
Example of change
of representation:
-- Packed_Descriptor and Descriptor are two different types
-- with identical characteristics, apart from their
-- representation
type Descriptor is
record
-- components of a descriptor
end record;
type Packed_Descriptor is new Descriptor;
for Packed_Descriptor use
record
-- component clauses for some or for all components
end record;
-- Change of representation can now be accomplished by explicit type conversions:
D : Descriptor;
P : Packed_Descriptor;
P := Packed_Descriptor(D); -- pack D
D := Descriptor(P); -- unpack P
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