Module: StateMachine::EvalHelpers

Included in:
Branch, Callback, Machine, StateContext
Defined in:
lib/state_machine/eval_helpers.rb

Overview

Provides a set of helper methods for evaluating methods within the context of an object.

Instance Method Summary (collapse)

Instance Method Details

- (Object) evaluate_method(object, method, *args, &block)

Evaluates one of several different types of methods within the context of the given object. Methods can be one of the following types:

  • Symbol

  • Method / Proc

  • String

Examples

Below are examples of the various ways that a method can be evaluated on an object:

class Person
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
end

class PersonCallback
  def self.run(person)
    person.name
  end
end

person = Person.new('John Smith')

evaluate_method(person, :name)                            # => "John Smith"
evaluate_method(person, PersonCallback.method(:run))      # => "John Smith"
evaluate_method(person, Proc.new {|person| person.name})  # => "John Smith"
evaluate_method(person, lambda {|person| person.name})    # => "John Smith"
evaluate_method(person, '@name')                          # => "John Smith"

Additional arguments

Additional arguments can be passed to the methods being evaluated. If the method defines additional arguments other than the object context, then all arguments are required.

For example,

person = Person.new('John Smith')

evaluate_method(person, lambda {|person| person.name}, 21)                              # => "John Smith"
evaluate_method(person, lambda {|person, age| "#{person.name} is #{age}"}, 21)          # => "John Smith is 21"
evaluate_method(person, lambda {|person, age| "#{person.name} is #{age}"}, 21, 'male')  # => ArgumentError: wrong number of arguments (3 for 2)


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# File 'lib/state_machine/eval_helpers.rb', line 53

def evaluate_method(object, method, *args, &block)
  case method
    when Symbol
      object.method(method).arity == 0 ? object.send(method, &block) : object.send(method, *args, &block)
    when Proc, Method
      args.unshift(object)
      arity = method.arity
      
      # Procs don't support blocks in < Ruby 1.9, so it's tacked on as an
      # argument for consistency across versions of Ruby
      if block_given? && Proc === method && arity != 0
        if [1, 2].include?(arity)
          # Force the block to be either the only argument or the 2nd one
          # after the object (may mean additional arguments get discarded)
          args = args[0, arity - 1] + [block]
        else
          # Tack the block to the end of the args
          args << block
        end
      else
        # These method types are only called with 0, 1, or n arguments
        args = args[0, arity] if [0, 1].include?(arity)
      end
      
      method.call(*args, &block)
    when String
      eval(method, object.instance_eval {binding}, &block)
    else
      raise ArgumentError, 'Methods must be a symbol denoting the method to call, a block to be invoked, or a string to be evaluated'
    end
end