Class: PiecePipe::AssemblyStep

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

Overview

A specialization of Step, designed to operate on subsets of input and add information to the flow. Inputs arrive as Hashes, and outputs are generated by (effectively) merging new key/value pairs on the Hash and producing the result.

Instead of implementing #process, AssemblySteps should implement #receive.

Instead of generating output with #produce, safely generate compound output by calling #install with a hash of one or more interesting values. As with process/produce, you may call #install zero or more times, depending on your need to filter, transform or expand the stream of objects.

The input to #receive is a duplicate of the actual Hash object that was produced by the previous step, so modifying the inputs directly will neither help you, nor harm subsequent steps.

AssemblySteps insist on consuming Hash-like objects; though the preceding step in the pipeline needn’t actually be an AssemblyStep, it must produce Hash-like objects as output.

#install starts with a fresh copy of the inputs each time, so multiple invocations will not share the installed values.

IF YOUR STEP DECIDES NOT TO INSTALL ANYTHING: be sure to call #noop (equiv to calling #install({})) which will pass all inputs on to the next step of the pipeline unmodified. If you DON’T call #install, your step effectively becomes a filter, and the flow of objects will cease.

Direct Known Subclasses

MethodAssemblyStep

Instance Attribute Summary

Attributes inherited from Step

#source

Instance Method Summary collapse

Methods inherited from Step

#to_enum

Instance Method Details

#install(value, opts = {}) ⇒ Object 



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# File 'lib/piece_pipe/assembly_step.rb', line 51

def install(value,opts={})
  output = @assembly.merge(value || {})
  
  if opts[:drop]
    opts[:drop].each do |key|
      output.delete(key)
    end
  end
  produce output
end

#noop ⇒ Object 



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# File 'lib/piece_pipe/assembly_step.rb', line 47

def noop
  install({})
end

#process(item) ⇒ Object 



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

def process(item)
  ensure_hash_like_object item
  @assembly = item
  begin
    receive(item)
  ensure
    @assembly = nil
  end
end

#receive(assembly) ⇒ Object

Default implementation is a noop



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# File 'lib/piece_pipe/assembly_step.rb', line 43

def receive(assembly)
  noop
end