Ruby Metaprograming and passing Parameters

Question

I want to define a method in ruby using

    define_method

within another function. Example code is below.

def demo(method_name)
    variable = 5
    define_method "#{method_name}" do
        #stuff
    end
end

Inside the newly defined method I want to be able to access the variable:

variable=5

that was previously defined. For example I want to be able to do :

    define_method "#{method_name}" do
        return variable*variable
    end

and get variable squared.

I want to be able to:

demo("squared")
x = squared # => 25

Is there a way I can pass the variable "variable" into the define_method even though it is not in the same scope?

Well, I am not sure but block do #stuff end is in the same scope as variable = 5. Even I am wrong, that block has access to a mother's scope*. Check this: a = 42; l =-> do; b = 22; l2 = -> do; puts a; end; end; l.call.call; *I am not sure about proper title so I made up that. — Darek Nędza
– Darek Nędza, Commented Jul 24, 2014 at 20:32
I'm confused. The code you have shown does exactly what you want. So, what is your question? — Jörg W Mittag
– Jörg W Mittag, Commented Jul 25, 2014 at 0:26

Nick Veys · Accepted Answer · 2014-07-24 20:18:20Z

4

Sure, and what you have works. What's the problem?

[15] pry(main)> def demo(method_name)    
[15] pry(main)*   variable = 5      
[15] pry(main)*   define_method "#{method_name}" do      
[15] pry(main)*     variable * variable        
[15] pry(main)*   end        
[15] pry(main)* end      
=> :demo
[16] pry(main)> demo('squared')
=> :squared
[17] pry(main)> squared
=> 25

answered Jul 24, 2014 at 20:18

Nick Veys

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