Defining the data structure

• Kind is represented by an enum, EType, containing the values kRock, kPaper, and kScissors.
• Color is represented by an instance of the class TRGBColor, which defines a color in a device-independent format. A TRGBColor instance can define any color, but initially this program defines the colors red, green, and blue.
• The size and position of the tile are stored in a single TGRect, representing the bounds of the tile.

NOTE The notation used in the CommonPoint documentation is described in "Reading notation diagrams" on page x of the Preface.

TaligentTypeExtension

The model for this program, TTilesModel, stores TTile instances in a collection and streams them in and out as part of the model. Because instances of the TTile class are saved as a persistent part of a Tiles document component, the TTile class needs to use TaligentTypeExtension, a facility that supports RTTI (Run Time Type Identification).

Classes that use RTTI require a set of utility functions. You can provide these supporting functions easily by calling the macro TaligentTypeExtensionDeclarationsMacro in your class header file, and the macro TaligentTypeExtensionMacro in the source file. These macros define functions that support versioning and that allow objects to be streamed in and out of persistent storage.

Classes that require RTTI must also define the following functions:

• Default and copy constructors
• Streaming operators (operator>>= and operator<<=)
• Assignment operator (operator=)

NOTE Often you can declare the assignment operator as a private function because it will never be used.

In addition to a default and copy constructor, TTile defines a constructor that lets you create a tile of a specific kind, color, size and position. This diagram shows the complete interface for the class TTile:

Storing the TTile objects

The TArrayOf<TTile> used by TTilesModel is constructed with a Nil comparator and a TMonomorphicStreamer<TTile>. It requires a streamer because the contents of the array are streamed when the model is streamed. See Chapter 1, "Collections," in Foundation Services for more information on these classes and on using collections.

To provide flexibility, it makes sense to allow the array to contain an arbitrary number of TTile instances. TTilesModel has two functions, AdoptTile and OrphanTile, that add a tile to or remove a tile from the model's array. In the first stage of developing this model, however, the number of tiles in the array is defined in the default constructor and is fixed at three. In a later step you'll see how to add the ability for the user to control the number of tiles in the array. (See "Ownership semantics" below for information on naming conventions for the AdoptTile and OrphanTile functions.)