ruby define_method dynamic block

Question

I have created a class dynamically, and am trying to add methods to the class. Assume a string represents the command needing to be evaluated by this method.

    a = "puts x"

    myobject.metaclass.send(:define_method, k){|x|
         // cannot do this, obviously 
         eval(a)
    }

Thanks for the help.

Edit:

k is coming from the file also, it would be trivial to just write the classes in ruby instead of reading an alternate file format as a class, but I want to make it as simple as possible to create the templates. looks something like...

generic

do_something:
  environment1:    
    foo arg1 arg2
  environment2:
    bar arg
    baz arg

I know what the method is called and what the method needs to do. I determine the appropriate environment for each class instance at runtime, I just can't seem to dynamically add statements to the method.

Can't you just eval a method string?

Dave Newton
– Dave Newton

2012-12-09 02:18:03 +00:00
Commented Dec 9, 2012 at 2:18 — Dave Newton
– Dave Newton, Commented Dec 9, 2012 at 2:18

Sean Hill · Accepted Answer · 2012-12-09 02:51:01Z

3

You can use class_eval.

a = <<-CODE
  def foo(x)
    puts x
  end
CODE

myobject.class.class_eval a

Update

Can you do something like this?

new_method = <<-CODE
  def #{k}(*args)
    #{a}
  end
CODE

myobject.class.class_eval new_method

Assuming you have:

k = some_method
a = puts args

new_method = <<-CODE
      def #{k}(*args)
        #{a}
      end
    CODE

myobject.class.class_eval new_method
myobject.some_method 1, "foo", "bar"

Then it would output:

1
foo
bar

edited Dec 9, 2012 at 2:51

answered Dec 9, 2012 at 2:25

Sean Hill

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6 Comments

Brandon Frohbieter Over a year ago

Thanks for the response. In this situation, a is non-mutable. I am parsing files created by ops guys, so I made the format have a simpler syntax. I've made it to the point where I have dynamically created the class and have an array of expressions as strings that I need to add to the respective method.

Sean Hill Over a year ago

Yeah, I know that. I was wondering where it is coming from. :-) Poorly worded the question, admittedly.

Sean Hill Over a year ago

Is the number of parameters to the method going to static?

Brandon Frohbieter Over a year ago

No, but I've omitted that detail for simplicity, figure I should be able to resolve that part with *args or something.

Brandon Frohbieter Over a year ago

removed - can't format in here, just going to expand on the initial question.

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