How to resolve the algorithm Polymorphic copy step by step in the BBC BASIC programming language

Published on 12 May 2024 09:40 PM
#Bbc basic

How to resolve the algorithm Polymorphic copy step by step in the BBC BASIC programming language

Table of Contents

Problem Statement

An object is polymorphic when its specific type may vary. The types a specific value may take, is called class. It is trivial to copy an object if its type is known: Here x is not polymorphic, so y is declared of same type (int) as x. But if the specific type of x were unknown, then y could not be declared of any specific type. The task: let a polymorphic object contain an instance of some specific type S derived from a type T. The type T is known. The type S is possibly unknown until run time. The objective is to create an exact copy of such polymorphic object (not to create a reference, nor a pointer to). Let further the type T have a method overridden by S. This method is to be called on the copy to demonstrate that the specific type of the copy is indeed S.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Polymorphic copy step by step in the BBC BASIC programming language

Source code in the bbc programming language

      INSTALL @lib$ + "CLASSLIB"
      
      REM Create parent class T:
      DIM classT{array#(0), setval, retval}
      DEF classT.setval (n%,v) classT.array#(n%) = v : ENDPROC
      DEF classT.retval (n%) = classT.array#(n%)
      PROC_class(classT{})
      
      REM Create class S derived from T, known only at run-time:
      RunTimeSize% = RND(100)
      DIM classS{array#(RunTimeSize%)}
      PROC_inherit(classS{}, classT{})
      DEF classS.retval (n%) = classS.array#(n%) ^ 2 : REM Overridden method
      PROC_class(classS{})
      
      REM Create an instance of class S:
      PROC_new(myobject{}, classS{})
      
      REM Now make a copy of the instance:
      DIM mycopy{} = myobject{}
      mycopy{} = myobject{}
      PROC_discard(myobject{})
      
      REM Test the copy (should print 123^2):
      PROC(mycopy.setval)(RunTimeSize%, 123)
      result% = FN(mycopy.retval)(RunTimeSize%)
      PRINT result%
      END

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