3. GNUstep for developers

From a developer's point of view, GNUstep provides an integrated makefile system, low-level and GUI libraries for application building, and a platform independant graphical rendering system.

The primary language used on GNUstep is Objective-C. It's a Smalltalk based set of extensions applied to ANSI C. It's object-oriented like Java and C++, but is a very dynamic language that uses a single inheritance model and allows protocols (or interfaces as known in Java). Unlike C++ which is completely staic, method calls in Objective-C are resolved at runtime and very loosely bound. This allows for certain things which are impossible in C++ without type-casting or cumbersome wrapper code and macros. Despite this, it is incredibly fast (being a compiled language) where method calls are about 2-3 times as slow as an ordinary C call, and where alot of optimisation is possible for further speed increases. It is not an interpreted bytecode language like Java.

It is a superset of C, which means that it doesn't interfere with ANSI C code and hence is completely compatible with any available C library. We use the gcc(1) set of compilers, and as of version 4.1.0, you can also mix Objective-C and Objective-C++ code in the same file. For those familiar with the language, it provides full category support (which means you can add code to classes in separate files or even at runtime) and can be optionally semi-staic bound.

3.1 gnustep-base (Foundation)

This is a library (or if you prefer, a framework) that provides the basic services needed in all applications, whether they be command-line or graphical. For developers, this is the common stuff found in ANSI C like

• string classes
• arrays and dictonarys (aka hash or map)
• file loading and saving
• time and dates handling
• filesystem manipulation

There's also more advanced classes which make it deadly simple to handle advanced issues such as

• object serialisation
• distributed objects (both cross-process and across networks)
• low and high level network communication
• XML parsing
• property lists

3.2 gnustep-gui (AppKit)

This library provides the Graphical User Interface (GUI) services needed for advanced application development. There are the usual control and window classes such as:

• abstract view representations
• buttons (including push-buttons, radio buttons, checkboxes, toggle buttons etc).
• static and user-editable text fields
• imageviews
• forms
• menus
• open and save dialogs
• scrollbars
• scroll views (hold views for easy adding of scroll support)
• slider controls
• tab views
• toolbars

There are also the more advanced GUI controls, some of which are not found on some other platforms including:

• browsers (which are great for representing hierachial data that needs to be constantly navigated, like filesystems)
• tableviews
• "matrix" controls (a set of controls layed out in a grid-like form).
• outline views (like the Windows TreeView control)
• clip views (holds a view which is clipped to the boundaries of its frame)
• rich text controls, which include built-in RTF support and advanced custom text-layout abilities

It also provides support for:

• drag and drop
• filter services
• pasteboards (cut and paste)
• colours and fonts
• document-centric applications
• drawing in customised views

User interfaces are stored in nib files, created by our interface builder, Gorm.app, which allows easy separation of interface and code. gnustep-gui uses the gnustep-back bundle to provide a clean abstraction between the user interface and the low-level drawing code.