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- lib/state_machine/eval_helpers.rb

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- #evaluate_method

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# StateMachine::EvalHelpers

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

### Public Instance Methods

evaluate_method(object, method, *args, &block) click to toggle source

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)

    # File lib/state_machine/eval_helpers.rb, line 53
    def evaluate_method(object, method, *args, &block)
      case method
        when Symbol
          klass = (class << object; self; end)
          args = [] if (klass.method_defined?(method) || klass.private_method_defined?(method)) && object.method(method).arity == 0
          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.is_a?(Proc) ? method.call(*args) : 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

[Validate]

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