language.md

Ruby Language Structure

This chapter describes the syntax constructs and general structure of Ruby programs.

As a brief overview, it can be said that:

• Ruby program consists of expressions dealing with literals, variables and constants.
• Expressions are:
  • assignments;
  • control expressions;
  • method calls;
  • definitions of modules, classes and methods.
• Ruby is an object-oriented language, so the program is structured by defining classes and modules and their methods.
  • Ruby has open classes that can be changed any time (even the core ones, like String). To localize class changes and implement hygienic extensions, one can use refinements.
• Error reporting and handling is done with exceptions.

Note that many of the language constructs you will see in a typical Ruby program, are in fact, just methods. For example Kernel#raise is used to raise an exception, and Module#private is used to change a method's visibility. As a result, the language core described in this chapter is pretty small, and everything else just follows usual rules for modules, methods and expressions.