VAR...IS

 Synopsis

         Define alternate name for inherited variable

 Syntax

         VAR <variable name> IS <original name>

 Arguments

         <variable name> is the alternative name that the inherited
         variable will be given in the current class

         <original name> is the name of an inherited variable (a
         variable defined in an ancestor class) which the declared
         alternative name will be mapped to.

 Description

         This command allows an alternative name to be defined for an
         existing variable. The existing variable must be defined in an
         ancestor class of the class being created. The command allows a
         class to be tailored so that its message names match its behavior.

 Example

         Assume that a Vehicle class defines a variable called width.
         We would like to define a subclass of Vehicle, called Boat.
         However, the width of a boat at its widest point is usually
         referred to as its beam. We could handle this by writing a
         method in the Boat class:

           METHOD beam
           RETURN ::width

         This handles access to the width variable via the beam
         message. As discussed under the MESSAGE...IS command, this
         could be done more efficiently in the class specification as
         follows:

           MESSAGE beam IS width

         However, neither of these solutions handles assignment via the
         beam message. To support assignment statements of the form:

           oBoat:beam := x

         we can use the VAR...IS command in the class specification as
         follows:

           CREATE CLASS Boat FROM Vehicle
              // ...
              VAR beam IS width

         This will allow both access and assignment to the width
         variable via the beam message.

 Note

         The VAR...IS command can only be used to define an alternative
         name for a variable in an ancestor class. Currently, an
         alternative name for a variable in the current class cannot be
         defined directly. A method can be defined to do this if necessary.

 See Also

         MESSAGE...IS