The Ruby Programming Language

Literals and Keyword Literals

Literals are values such as 1.0, 'hello world', and [] that are embedded directly into your program text. We introduced them in Chapter 2 and documented them in detail in Chapter 3.

It is worth noting that many literals, such as numbers, are primary expressions—the simplest possible expressions not composed of simpler expressions. Other literals, such as array and hash literals and double-quoted strings that use interpolation, include subexpressions and are therefore not primary expressions.

Certain Ruby keywords are primary expressions and can be considered keyword literals or specialized forms of variable reference:

nil	Evaluates to the nil value, of class NilClass.
true	Evaluates to the singleton instance of class TrueClass, an object that represents the Boolean value true.
false	Evaluates to the singleton instance of class FalseClass, an object that represents the Boolean value false.
self	Evaluates to the current object. (See Chapter 7 for more about self.)
__FILE__	Evaluates to a string that names the file that the Ruby interpreter is executing. This can be useful in error messages.
__LINE__	Evaluates to an integer that specifies the line number within __FILE__ of the current line of code.
__ENCODING__	Evaluates to an Encoding object that specifies the encoding of the current file. (Ruby 1.9 only.)