In addition to the standard C function libraries and specialized function libraries for the Macintosh (which call the Macintosh Toolbox ROM routines), Think C comes with the Think Class Library (TCL). The TCL is made up of several source files containing method definitions for several useful classes, which are themselves defined in TCL header files.
These classes can be used to declare the objects which make up the graphical user interface for Macintosh programs. TCL classes encapsulate the data and functionality needed to implement an event-driven Application dealing with Files, Windows, ScrollBars, Pictures, EditText fields, CheckBoxes, etc. (See the TC manuals.)
In this way the complexities of the Macintosh graphical user interface are "hidden" from the programmer, yet the programmer has the ability to derive new classes from the TCL classes to obtain specialized functionality. This feature of the OOP approach cannot be obtained using traditional function libraries.
The potential exists for the standardization of class libraries such as the TCL, to allow cross-platform development using graphical user interfaces*.
