Inheritance and Modules

Constants and Namespaces

Modules can group constants and classes under a qualified name.

namespace A module name can act as a namespace for constants and classes that belong together.

Constants and Namespaces

subtotal
constants_namespaces.rb
Replay: real traced execution (multi-file project)
module Store
  TAX_PERCENT = 8

  class Calculator
    def self.total(subtotal)
      subtotal + subtotal * TAX_PERCENT / 100
    end
  end
end

subtotal = 25
total = Store::Calculator.total(subtotal)

puts "tax_percent=#{Store::TAX_PERCENT}"
puts "subtotal=#{subtotal}"
puts "total=#{total}"

module Store
  TAX_PERCENT = 8

  class Calculator
    def self.total(subtotal)
      subtotal + subtotal * TAX_PERCENT / 100
    end
  end
end

subtotal = 10
total = Store::Calculator.total(subtotal)

puts "tax_percent=#{Store::TAX_PERCENT}"
puts "subtotal=#{subtotal}"
puts "total=#{total}"

module Store
  TAX_PERCENT = 8

  class Calculator
    def self.total(subtotal)
      subtotal + subtotal * TAX_PERCENT / 100
    end
  end
end

subtotal = 40
total = Store::Calculator.total(subtotal)

puts "tax_percent=#{Store::TAX_PERCENT}"
puts "subtotal=#{subtotal}"
puts "total=#{total}"

  1. TAX_PERCENT ← 8, subtotal ← 25

    1module Store2  TAX_PERCENT→ 8 = 834  class Calculator5    def self.total(subtotal)6      subtotal + subtotal * TAX_PERCENT / 1007    end8  end9end1011subtotal→ 25 = 25  #@subtotal=10, 4012total = Store::Calculator.total(subtotal)27

  2. def self.total(subtotal)

    4class Calculator5  def self.total(subtotal25)6    subtotal25 + subtotal * TAX_PERCENT8 / 1007  end

  3. total ← 27

    11subtotal = 25  #@subtotal=10, 4012total→ 27 = Store::Calculator.total(subtotal)271314puts "tax_percent=#{Store::TAX_PERCENT8}"15puts "subtotal=#{subtotal25}"16puts "total=#{total27}"
    outputtax_percent=8
subtotal=25
total=27

  1. TAX_PERCENT ← 8, subtotal ← 10

    1module Store2  TAX_PERCENT→ 8 = 834  class Calculator5    def self.total(subtotal)6      subtotal + subtotal * TAX_PERCENT / 1007    end8  end9end1011subtotal→ 10 = 1012total = Store::Calculator.total(subtotal)10

  2. def self.total(subtotal)

    4class Calculator5  def self.total(subtotal10)6    subtotal10 + subtotal * TAX_PERCENT8 / 1007  end

  3. total ← 10

    11subtotal = 1012total→ 10 = Store::Calculator.total(subtotal)101314puts "tax_percent=#{Store::TAX_PERCENT8}"15puts "subtotal=#{subtotal10}"16puts "total=#{total10}"
    outputtax_percent=8
subtotal=10
total=10

  1. TAX_PERCENT ← 8, subtotal ← 40

    1module Store2  TAX_PERCENT→ 8 = 834  class Calculator5    def self.total(subtotal)6      subtotal + subtotal * TAX_PERCENT / 1007    end8  end9end1011subtotal→ 40 = 4012total = Store::Calculator.total(subtotal)43

  2. def self.total(subtotal)

    4class Calculator5  def self.total(subtotal40)6    subtotal40 + subtotal * TAX_PERCENT8 / 1007  end

  3. total ← 43

    11subtotal = 4012total→ 43 = Store::Calculator.total(subtotal)431314puts "tax_percent=#{Store::TAX_PERCENT8}"15puts "subtotal=#{subtotal40}"16puts "total=#{total43}"
    outputtax_percent=8
subtotal=40
total=43