Reference

Keywords

Ruby keywords and special language constructs.

1. Global Variables

   Global variables in Ruby use a $ prefix, stay visible across scopes, and should be reserved for rare program-wide state.

   $variable_name
2. Ruby keyword: case

   Ruby case expression: subject form vs no-subject form, === matching, multiple when values, then/else, return value, common gotchas.

   case subject when pat[, pat]* [then] body [when ...]* [else body] end | case when expr [then] body ... end
3. Ruby keyword: class

   The Ruby class keyword defines, reopens, and extends classes — including singleton classes via class << obj. Syntax, return value, and gotchas.

   class Name
4. Ruby keyword: def

   The def keyword defines methods in Ruby — instance, class, singleton, and operator methods — with positional, keyword, splat, and block parameters.

   def name([params]) [body] end
5. Ruby keyword: if

   Ruby if expression: syntax for if, elsif, else, ternary, and modifier-if forms, with truthy rules and return value behavior.

   if expr then body [elsif expr then body]* [else body] end | body if expr
6. Ruby keyword: module

   The Ruby module keyword creates a Module for namespacing and mix-ins. Covers syntax, nesting, reopening, and gotchas vs class.

   module Name [:: Nested]
7. Ruby keyword: unless

   Ruby unless expression: block form, modifier form, else rules, truthy/falsy rules, return value, and common parser gotchas.

   unless expr then body [else body] end | body unless expr
8. Ruby keyword: until

   Ruby's until keyword loops while a condition is false. Block form, modifier form, begin/end variant, return value, and break/next/redo interaction.

   until expr [do] ... end
9. Ruby keyword: when

   Ruby when clause inside case: === matching, multiple patterns per when, then/else, regex/range/module/proc matchers, and how it differs from if.

   when expr [, expr]* [then] body
10. Ruby keyword: while

    Ruby's while keyword loops while a condition stays true. Syntax, modifier form, begin/end variant, return value, and break/next/redo interaction.

    while expr [do] ... end