Class: Cuprum::Command

Inherits:
Object
  • Object
show all
Includes:
Chaining, Processing
Defined in:
lib/cuprum/command.rb

Overview

Functional object that encapsulates a business logic operation with a consistent interface and tracking of result value and status.

A Command can be defined either by passing a block to the constructor, or by defining a subclass of Command and implementing the #process method.

Examples:

A Command with a block

double_command = Cuprum::Command.new { |int| 2 * int }
result         = double_command.call(5)

result.value #=> 10

A Command subclass

class MultiplyCommand < Cuprum::Command
  def initialize multiplier
    @multiplier = multiplier
  end # constructor

  private

  def process int
    int * @multiplier
  end # method process
end # class

triple_command = MultiplyCommand.new(3)
result         = command_command.call(5)

result.value #=> 15

A Command with an error state

class DivideCommand < Cuprum::Command
  def initialize divisor
    @divisor = divisor
  end # constructor

  private

  def process int
    if @divisor.zero?
      return Cuprum::Result.new(error: 'errors.messages.divide_by_zero')
    end

    int / @divisor
  end # method process
end # class

halve_command = DivideCommand.new(2)
result        = halve_command.call(10)

result.error #=> nil
result.value #=> 5

divide_command = DivideCommand.new(0)
result         = divide_command.call(10)

result.error #=> 'errors.messages.divide_by_zero'
result.value #=> nil

Command Chaining

class AddCommand < Cuprum::Command
  def initialize addend
    @addend = addend
  end # constructor

  private

  def process int
    int + @addend
  end # method process
end # class

double_and_add_one = MultiplyCommand.new(2).chain(AddCommand.new(1))
result             = double_and_add_one(5)

result.value #=> 5

Conditional Chaining

class EvenCommand < Cuprum::Command
  private

  def process int
    return int if int.even?

    Cuprum::Errors.new(error: 'errors.messages.not_even')
  end # method process
end # class

# The next step in a Collatz sequence is determined as follows:
# - If the number is even, divide it by 2.
# - If the number is odd, multiply it by 3 and add 1.
collatz_command =
  EvenCommand.new.
    chain(DivideCommand.new(2), :on => :success).
    chain(
      MultiplyCommand.new(3).chain(AddCommand.new(1),
      :on => :failure
    )

result = collatz_command.new(5)
result.value #=> 16

result = collatz_command.new(16)
result.value #=> 8

See Also:

Instance Method Summary collapse

Methods included from Chaining

#call, #chain, #chain!, #tap_result, #tap_result!, #yield_result, #yield_result!

Methods included from Processing

#arity, #call, #process

Constructor Details

#initialize {|*arguments, **keywords, &block| ... } ⇒ Command

Returns a new instance of Cuprum::Command.

Yields:

  • (*arguments, **keywords, &block) —

    If a block is given, the #call method will wrap the block and set the result #value to the return value of the block. This overrides the implementation in #process, if any.



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# File 'lib/cuprum/command.rb', line 122

def initialize &implementation
  return unless implementation

  define_singleton_method :process, &implementation

  singleton_class.send(:private, :process)
end