Polymorphic copy: Difference between revisions

Line 26:

end Base;

use Base;

package body Base is

function Name (X : T) return String is

Line 33:

end Name;

end Base;

-- The procedure knows nothing about S

procedure Copier (X : T'Class) is

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function Clone (X : T'Class) return T_ptr is

begin

return new T'Class(X);

return new T'Class'(X);

end ~~Copier~~;

end Clone;

package Derived is

type S is new T with null record;

overriding function Name (X : S) return String;

end Derived;

use Derived;

package body Derived is

function Name (X : S) return String is

begin

Line 62:

Object_1 : T;

Object_2 : S;

Object_3 : T_ptr := Clone(T);

Object_3 : T_ptr := Clone(Object_1);

Object_4 : T_ptr := Clone(S);

Object_4 : T_ptr := Clone(Object_2);

begin

Copier (Object_1);

Line 69:

Put_Line ("Cloned " & Object_3.all.Name);

Put_Line ("Cloned " & Object_4.all.Name);

end Test_Polymorphic_Copy;~~</syntaxhighlight>~~

end Test_Polymorphic_Copy;

</syntaxhighlight>

The procedure Copier does not know the specific type of its argument.

Nevertheless it creates an object Duplicate of exactly same type.

Nevertheless, it creates an object Duplicate of exactly the same type. The function Clone makes a copy in the heap with the correct type and returns a pointer to it.

<pre>