Learn to Program

The instance variable enables individual objects to remember state. Instance variables work much like other variables: you assign values to them, and you read those values back; you can add them together, print them out, and so on. But instance variables have a few differences: Instance variable names always start with a single @ (at sign). This en

This example also illustrates the fact that all the code in class- and module-definition blocks gets executed when it’s first encountered, whereas methods aren’t executed until an object is sent the appropriate message. That’s why the value of a that’s set inside the show_a method is displayed last among the five values that the program prints; the

From our earliest examples onward, we’ve been making bareword-style calls to puts and print, like this one: puts "Hello" puts and print are built-in private instance methods of Kernel—not, like the ones you write, of Object, but of Kernel. The upshot is similar, though (because Object mixes in Kernel): you can call such methods at any tim

The Ruby interpreter starts up with a fairly large number of global variables already initialized. These variables store information that’s of potential use anywhere and everywhere in your program.