Object Example: a Trumpet

The following is an example of a Carapace object. This Trumpet object describes a trumpet (ie. the musical instrument) which can be muted (ie. have a mute stuffed in the end to change the sound) or open (no mute).

(class "Trumpet"

    (interface

        (properties

            (mute String)
            (metal String readOnly)
        )

        (methods

            # constructor function - used when creating a Trumpet
            (NIL Trumpet ( (m String) ) )

            # play a piece of music
            (NIL play ( (m Music) ) )
        )
    )
)

• the class has a name: Trumpet
• the method used to initialise an object of this type has the same name as the class. It returns no value NIL and, in this example, takes a single argument which is the type of metal from which the trumpet is made.
• the 'play' method takes a single argument which is of type Music.
• the 'metal' property is readOnly meaning that it cannot be altered by anyone accessing the property directly. In Carapace, readOnly attributes can only be changed by the object methods. In this example, the type of metal is set when the Trumpet is created - the same as in the real world
• the 'mute' property can be changed by anyone accessing the object. There are various sorts of mute for a trumpet eg. Straight, Cup.

An Additional Interface

Our Trumpet object is pretty good - it can already play music - but suppose the people living in the same house wanted some sort of control over the trumpet. These people don't want to play the trumpet - they just want to control its volume. This could be done by having an additional interface on our Trumpet object eg.:

    (interface

        (methods

            # set the maximum volume
            (NIL setVolume ( (max Integer) ) )

            # make it silent!
            (NIL silencer () )
        )
    )

(class "Trumpet"

    (interface

        (properties

            (mute String)
            (metal String readOnly)
        )

        (methods

            # initialise the object
            (NIL Trumpet ( (m String) ) )

            # play a piece of music
            (NIL play ( (m String) ) )
        )
    )

    (interface Volume

        (methods

            # set the maximum volume
            (NIL setVolume ( (max Integer) ) )

            # make it silent!
            (NIL silencer () )
        )
    )
)

For a complete description of object definition, click here

Accessing a Trumpet via COM

By adding a few more details to our Trumpet example above, we can access it from COM.

To see what is required, click here.