From: Richard Crowley <r@...>
Date: 2008-10-25T02:55:13+09:00
Subject: Object#instance_eval but better

I have a bit of code here that I'd love to make better:

class Foo
     def initialize(path)
         self.instance_eval(File.read(path))
     end
end

I don't want to continue down the path of reading an entire file into a 
string and then eval'ing that string just to get the contents of the 
file executed as if it were the body of a method in a class.  The file 
passed to the constructor above might contain something like:

@foo = 'This will become an instance variable when you do Foo.new(path)'

I've tried all manner of hacks to make Kernel#load and friends execute 
code as if it were in the calling scope.  In every case I've seen the 
loaded file leave no lasting effect on the instance variables of the 
calling method.  My goal is to be able to do exactly this:

class Foo
     def initialize(path)
         load_in_scope path
     end
end
f = Foo.new('load_me.rb')
f.instance_variables # => ['@foo']

My assumption here is that reading a file into a string and eval'ing it 
is very slow and is bad form.  Am I right?

Is this possible without reading the file into a string?  Is this 
possible without hacking the C code?  Should I go bother ruby-core?

Thanks,

Richard