13.6 Change of Representation

1. A type_conversion, See section 4.6 Type Conversions 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 need to be declared with matching component subtypes, and convertible index types. If one type has packing specified and the other does not, then explicit conversion can be used to pack or unpack an array.
2. To convert a record from one representation to another, two record types with a common ancestor type need to be declared, with no inherited subprograms. 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
   
3. Example of change of representation:

4. -- Packed_Descriptor and Descriptor are two different types
   -- with identical characteristics, apart from their
   -- representation
   

5. type Descriptor is
       record
         -- components of a descriptor
       end record;
   

6. type Packed_Descriptor is new Descriptor;
   

7. for Packed_Descriptor use
       record
         -- component clauses for some or for all components
       end record;
   

8. --  Change of representation can now be accomplished
   --  by explicit type conversions:
   

9. D : Descriptor;
   P : Packed_Descriptor;
   

10. P := Packed_Descriptor(D);  -- pack D
    D := Descriptor(P);         -- unpack P
    

Go to the first, previous, next, last section, table of contents.