Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Ruby Variable Scopes

Miha Rekar
January 20, 2015

Ruby Variable Scopes

Miha Rekar

January 20, 2015
Tweet

More Decks by Miha Rekar

Other Decks in Programming

Transcript

  1. RUBY VARIABLE SCOPES

  2. SCOPES • Local Variables • Instance Variables • Class Variables

    • Class Instance Variables • Global Variables • Constants
  3. LOCAL VARIABLES • “normal” • x = 25 • local

    to a method/block/class declaration • goes away when its scope closes
  4. INSTANCE VARIABLES • prefixed with `@` • @name = ‘Miha’

    • available inside an instance scope • each instance has a separate value
  5. CLASS VARIABLES • prefixed with `@@` • @@gears = 5

    • available inside a class and instance scope • same for all instances • same for superclass and subclasses
  6. CLASS VARIABLES EXAMPLE class Polygon @@sides = 10 def self.sides

    @@sides end end puts Polygon.sides # => 10 class Triangle < Polygon @@sides = 3 end puts Triangle.sides # => 3 puts Polygon.sides # => 3
  7. CLASS INSTANCE VARIABLES • classes are objects too • prefixed

    with `@` • @cards = 52 • available anywhere inside a class scope • NOT same for superclass and subclasses
  8. CLASS INSTANCE VARIABLES EXAMPLE class Polygon @sides = 8 def

    self.sides @sides end def sides @sides end end puts Polygon.sides # => 8 puts Polygon.new.sides # => nil class Triangle < Polygon @sides = 3 end puts Triangle.sides # => 3 puts Polygon.sides # => 8
  9. GLOBAL VARIABLES • prefixed with `$` • $HOME = ‘Ljubljana’

    • should be used sparingly • available everywhere • can be traced
  10. CONSTANTS • begin with a capital letter • upper snake

    case by convention • I_AM_A_CONSTANT = 25 • supposed to remain constant
  11. CONSTANTS EXAMPLE [1] pry(main)> A_CONST = 10 => 10 [2]

    pry(main)> A_CONST = 20 (pry):50: warning: already initialized constant A_CONST (pry):49: warning: previous definition of A_CONST was here => 20 [3] pry(main)> A_CONST => 20
  12. THANKS