class Patterns::Command

Command -> Object

Base Class that acts as a receiver and allows execution for a command while also storing status and description All of this class' subclasses may optionally implement undo, which is an example of the Memento Pattern. Memento will be covered more fully in the Abstract State Machine/Finite State Machine pattern.

From Design Patterns (Gang of Four)

- • Command – declares an interface for executing an operation.

Attributes

description[RW]

stores the description that is passed to the initializer upon object instantiation

status[RW]

the most recent status of the command

Public Class Methods

new(description) click to toggle source

Initializes the Command Class Designed to be called by a child class in its initialize method

  • description - The description of the sub class

Examples

=> #inside child class
=> def initialize
=>  desc = 'A new child class of Command'
=>  super(desc) # (calls the super class' initialize function defined below)
=> end

# File app/models/command/command.rb, line 30
def initialize(description)
  @description = description
  @status = 'initialized'
end

Public Instance Methods

execute(function) click to toggle source

Called by the child class' execute function

  • function - The actual command that will be executed, passed in from the sub class

Examples

=> #inside child class, look at create_file.rb, copy_file.rb, or delete_file.rb for a complete example
=> def execute
=>  function = Proc.new do # or Proc.new {}
=>    #code to be executed
=>  end
=>  super(function) # (calls the super class' execute function defined below)
=> end

# File app/models/command/command.rb, line 48
def execute(function)
  @status = "Command began: #{@description}"
  function.call
  @status = "Execution completed: #{@description}"
end
undo(function) click to toggle source

Called by the child class' undo function.

  • function - The command that will perform the undo operation

Examples

=> #inside child class
=> def undo
=>  function = Proc.new do
=>    #code to undo execute function
=>  end
=> super(function) # (calls the super class' undo function defined below)
=> end

# File app/models/command/command.rb, line 67
def undo(function)
  @status = "Undo began: #{@description}"
  function.call
  @status = "Undo completed: #{@description}"
end