Module: StateMachines::EvalHelpers

Included in:
Branch, Callback, Machine, StateContext
Defined in:
lib/state_machines/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

#evaluate_method(object, method, *args, **kwargs, &block) ⇒ Object

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)



55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
 
# File 'lib/state_machines/eval_helpers.rb', line 55

def evaluate_method(object, method, *args, **kwargs, &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, **kwargs, &block)
    when Proc
      args.unshift(object)
      arity = method.arity
      # Handle blocks for Procs
      if block_given? && 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

    # Call the Proc with the arguments
    method.call(*args, **kwargs)

    when Method
      args.unshift(object)
      arity = method.arity

      # Methods handle blocks via &block, not as arguments
      # Only limit arguments if necessary based on arity
      args = args[0, arity] if [0, 1].include?(arity)

      # Call the Method with the arguments and pass the block
      method.call(*args, **kwargs, &block)
    when String
      if block_given?
        if StateMachines::Transition.pause_supported?
          eval(method, object.instance_eval { binding }, &block)
        else
          # Support for JRuby and Truffle Ruby, which don't support binding blocks
          eigen = class << object; self; end
          eigen.class_eval <<-RUBY, __FILE__, __LINE__ + 1
              def __temp_eval_method__(*args, &b)
                #{method}
              end
            RUBY
          result = object.__temp_eval_method__(*args, &block)
          eigen.send(:remove_method, :__temp_eval_method__)
          result
        end
      else
        eval(method, object.instance_eval { binding })
      end
    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