Ruby is a powerful object-oriented scripting language that has been rapidly growing in popularity. It was developed by Yukihiro “Matz” Matsumoto in the early 90’s and has a vibrant community of users and enthusiasts.

As an increasingly grey-haired software developer, I’ve found some things in Ruby that make me like it a lot:

• Everything is an object. No more having to remember what’s an object and what’s a built-in type (as in Python). Everything can accept messages, which makes code easier to write and more consistent overall.

• All constructs have values. As above, no more remembering whether some specific function returns a value or not. This also allows us to write nice tight expressions like this:

myList.sort.uniq.each {|x| puts x.length}

• I can interact with Ruby and the programs I write in Ruby using irb, the interactive Ruby console.

• Ruby is introspective. At runtime I can easily ask objects their type and what messages they accept. In fact, because of this capability, the type of an object is of secondary importance: what matters most is the set of messages that an object can handle. Ruby documentation author Dave Thomas called this “duck typing”, because “if it walks like a duck, and talks like a duck, then it might as well be a duck.”

• Ruby makes it easy to add domain-specific extensions. This means that I don’t have to write parsers for custom languages and don’t need to use special-purpose command languages like Tcl (which have a tendency to “creep up” and turn into programming languages when users start writing 10,000 lines of customization!)

• I can easily extend existing classes. Ruby classes are open; at any time or place a Ruby program can add a new declaration of an existing class that adds or modifies its methods. This provides programmers with an easy way to add new convenience methods to classes and to work around problems quickly.

• I can use Ruby for nearly everything: builds, web programming, application programming, system programming. The Ruby community is bustling with activity; people are applying Ruby to new problems all the time and a lot of code is being shared.

And the reason I started using RubyCocoa:

• Using RubyCocoa and Objective-C, I can easily mix Ruby and compiled C and C++ code.

Objective-C is an object-oriented extension of C that is derived from SmallTalk. It was developed by Brad Cox in the early 1980’s around the same time that C++ was becoming popular.

Both Objective-C and C++ added object-oriented features to C, but did so in very different ways. C++ emphasized static type-safety: objects were defined with fixed types and the correctness of their interactions was checked during program compilation. As a result, after a program was compiled, little information about the types of objects was kept—all that was needed was implicit in the compiled object code. In contrast, Objective-C was designed to be a dynamically-typed language in which the types of objects could vary at runtime. This made it necessary for compiled programs to keep a lot of information about the types of objects, most notably the messages that objects accept.

An Objective-C message is similar to a function call but more flexible. When a message is sent to an Objective-C object, the receiver may or may not be able to respond to it. If it is an unsupported message, an object may have a generic handler that can forward the message to another object, sometimes called its delegate. To support this and other dynamic capabilities, compiled Objective-C programs contain tables of type information that can be used to inquire whether or not certain messages are supported, to list the messages that may be sent to an object, and even to dynamically add support for additional messages. As we will see, these tables make Objective-C an ideal companion to Ruby.

Cocoa is a framework for building desktop applications. It was originally developed by NeXT Computer, Inc. in the 1990’s and is currently available for computers running Mac OS X. It is built on Objective-C and provides a rich collection of objects that correspond to user interface elements such as windows, views, and controls.

Cocoa is used by the majority of the OS X applications shipped by Apple and its third-party developers. Virtually every beautiful user interface feature that you see in Macintosh applications is directly available through the Cocoa interfaces.