CODEWITHSUNDEEP
rubymethodsmetaprogrammingeval
Bogdan Gusiev
Bogdan Gusiev

Reputation: 8305

Ruby performance: define method with define_method or eval

While looking through ActiveSupport source code I've noticed that sometimes eval is used in places where define_method is enough.

Example: ActiveSupport: Module.delegate

I consider define_method more clean and safe way of doing things. What is the benefits of eval over define_method? Perfomance, memory usage, something else?

Upvotes: 7

Views: 1662

Answers (3)

Victor Deryagin
Victor Deryagin

Reputation: 12225

I don't know what the reason in that particular case, but define_method takes a block, which is a closure (carries local variables of the place it was defined), and that can lead to considerably higher memory consumption comparing to plain eval.

Upvotes: 2

emboss
emboss

Reputation: 39620

I found this to be a very nice article on the subject: http://blog.grayproductions.net/articles/eval_isnt_quite_pure_evil.

Upvotes: 3

Andrew Grimm
Andrew Grimm

Reputation: 81510

When you use define_method, the method you're defining can't accept a block.

It’s pretty well known that because of a deficiency in blocks arguments in Ruby 1.8 Class#define_method cannot define methods that take blocks.

def x *args, █ end  # => works!
define_method(:x) {|*args,&block| } # => SyntaxError: compile error

The method being defined requires a block:

"def #{prefix}#{method}(*args, &block)" # def customer_name(*args, &block)

So define_method can't be used.

Upvotes: 3

Related Questions