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Global Variable

• name starts with $:
  • $foo

Instance Variable (variable member of a class)

• name starts with @:
  • @bar

Class variable

• A Ruby Class Variable is like a C++ static data member. There is only one variable. That variable is accessable by all instances of the class.
• A class variable name starts with two 'at' signs:
  • @@number_of_things
• Class variables must be initialized before they are used. This can be done in the class definition:

  class Song
    @@plays = 0
  ...
  

Local Variable

• name starts with lower case letter:
  • foo

Constants

• Constants aren't really, you only get a warning if you change the value.
• The name of constants start with an upper case letter:
  • This_Constant = 1

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