Class: PiecePipe::MethodStep

Inherits:
Step
  • Object
show all
Defined in:
lib/piece_pipe/method_step.rb

Overview

MethodStep makes it possible to define a pipeline step by wrapping a Method object. Eg,

PiecePipe::Pipeline.new.step( method(:do_something) )

In this contrived example, whatever class is building the Pipeline has a #do_something method, which is accessed as a Method object from Ruby’s reflection API via Kernel#method.

If the wrapped method accepts a single parameter (arity 1), the inputs to your MethodStep will be passed in via this parameter, and the return value of your method will be automatically #produced, even if you return nil.

If the wrapped method accepts TWO parameters (arity 2), the inputs will still arrive via the first paramter, and the second parameter will be a “producer” object that responds to #produce. This gives you the flexibility to #produce zero-or-many items, as in normal Step subclasses. In the case of arity-2 methods, the return value is disregarded. Failing to call producer#produce will result in a filtering-out of objects.

Instance Attribute Summary

Attributes inherited from Step

#source

Instance Method Summary collapse

Methods inherited from Step

#to_enum

Constructor Details

#initialize(meth) ⇒ MethodStep

Returns a new instance of MethodStep.



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# File 'lib/piece_pipe/method_step.rb', line 24

def initialize(meth)
  raise "method cannot be nil" if meth.nil?
  raise "method must accept 1 or 2 arguments; it accepts #{meth.arity}" if meth.arity != 1 and meth.arity != 2
  @method = meth
end

Instance Method Details

#process(item) ⇒ Object 



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# File 'lib/piece_pipe/method_step.rb', line 32

def process(item)
  case @method.arity
  when 1
    # The method takes 1 argument, which we assume to be the input item.
    # We also assume that the method RETURNS the ONLY item it wishes to produce.
    # Will always produce exactly 1 output, even if that's just nil.
    produce @method.call(item)
  when 2
    # The method takes 2 arguments.  Assume first is input item, second is "producer",
    # ie, a means for the method to produce 0, 1 or many outputs at its discretion.
    # (by calling producer.produce)
    # Return value of @method.call is NOT considered.
    @method.call item, self
  end
end