Where is Ruby code, generated via metaprogramming, stored, and is it viewable/printable?

StackOverflow https://stackoverflow.com/questions/17448512

質問

I've just started learning about metaprogramming in Ruby, and found myself wondering if it was possible to view (in someway) the code that had been generated. I want to, as a coding exercise, write a short method that will generate a Ruby file containing either a few method definitions or, ideally, an entire class or module definition.

I was thinking that perhaps just building up a string representation of the file and then merely writing it out might be a way to accomplish that, but that way doesn't really necessitate the use of metaprogramming, and since my goal is a metaprogramming exercise, I would like to figure out a way to incorporate it into that process or else do it another way.

I guess, if I was to take the string-building approach, I would like to start with something like

klass_string = "class GeneratedClass\n\t<BODY>\nend"

and then somehow save the output of something like this

define_method( :initialize ) do
  instance_variable_set("@var", "some_value")
end

in a string that could replace '' in klass_string and then written out to a file. I know I could just put the above code snippet directly into the string, and it would workout fine, but I would like to have the output in a more standard format, as if it'd been written by hand and not generated:

class GeneratedClass
  def initialize
    @var = 'some_value'
  end
end

Could someone point me in the right direction?

役に立ちましたか？

解決

I agree with your comment that this question isn't really about metaprogramming so much as dynamic code generation / execution and introspection. Those are interesting topics, but not really metaprogramming. In particular your question about outputting ruby code to strings is about introspection, where as your string injection question is about dynamic code (just to try give you the words to google about what you're interested in).

Since your question is general and really around introspection and dynamic code, I'm going to reference you to some canonical and useful projects that can help you learn more..

ParseTree & Ruby Parser and Sourcify

Ruby Parser is a pure ruby implementation of ParseTree, so I'd recommend starting there to learn how to examine and "stringify" Ruby code. Play around with all of those, and in particular learn how they examine code in Ruby to generate their results. You'll learn a ton about how things work under the hood. Eric Hodel among others is real smart about this stuff.. Be warned though, this is really advanced stuff, but if that's where you want to build expertise, hopefully those references will help!

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