Dynamically Create Class. (or. Why is eval() messy?)

ruby-talk
1

Hi,
I'm trying to create a utility method that will automatically create a
class for me, given a classname. But I can't find a way around having to
use eval().

This is what I'm doing right now:

def createClass(className)
  eval(<<-EOS)
    #{className} = Class.new do
      #bla bla bla
    end
  EOS
end

but I really don't like eval() and would like to avoid it, if at all
possible.

Is there a reason, that Ruby doesn't support something like this: Maybe
because it's inconsistent with something, or because it's really hard?

className = "MyClass"
methodName = "myMethod"

class *className
  def *methodName
    puts "yay!"
  end
end

Also, I find eval() code really messy. Though I'm not sure why. I think
I don't like it, because my editor (IntelliJ) doesn't do syntax
highlighting for strings. Do you guys know of any editors that will
syntax highlight a eval() string for you?

···

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2

You're almost there. This works

def create_class name, mod = Object
  cls = Class.new do
    ...
  end
  mod.constant_set name, cls
end

This allows to put the created class inside any module/class you like. If you
don't need it, simply remove it from the argument list and use Object in its
place inside the method.

I hope this helps

Stefano

···

On Wednesday 20 August 2008, Patrick Li wrote:

Hi,
I'm trying to create a utility method that will automatically create a
class for me, given a classname. But I can't find a way around having to
use eval().

This is what I'm doing right now:

def createClass(className)
  eval(<<-EOS)
    #{className} = Class.new do
      #bla bla bla
    end
  EOS
end

but I really don't like eval() and would like to avoid it, if at all
possible.

3

Ah =), that's quite lovely. Thank you.
Until you suggested that, I was almost contemplating switching to Lisp
or something.

···

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