When passing objects as parameters, are they passed by reference?

Question

Is there any performance implications if I do either of these:

def do_something(user, article)
...
end

versus

def do_someth         


        

Answer 1

Re: https://stackoverflow.com/a/6528257 (I didn't have enough reputation to comment at time of writing)

Ah, but Jörg, if you actually manipulate the argument, instead of assigning a new object to it, the method behaves differently. Using .replace instead of = gives you this:

def is_Ruby_pass_by_value_or_reference?(parameter)
  parameter.replace 'Ruby is pass-by-reference.'
end

var = 'Ruby is pass-by-value.'

is_Ruby_pass_by_value_or_reference?(var)

puts var
# Ruby is pass-by-reference.

In fact, let's elaborate just a little more, just to show the difference:

def is_Ruby_pass_by_value_or_reference?(parameter)
  parameter.replace 'Ruby is pass-by-reference.'
  parameter = "This assigns a whole new object to 'parameter', but not to 'var'."
  puts parameter
end

var = 'Ruby is pass-by-value.'

is_Ruby_pass_by_value_or_reference?(var)
# This assigns a whole new object to 'parameter', but not to 'var'.

puts var
# Ruby is pass-by-reference.

Answer 2

No, Ruby never passes by reference. Ruby is pass-by-value. Always. No exceptions.

def is_Ruby_pass_by_value_or_reference?(parameter)
  parameter = 'Ruby is pass-by-reference.'
end

var = 'Ruby is pass-by-value. Always. No exceptions.'

is_Ruby_pass_by_value_or_reference?(var)

puts var
# Ruby is pass-by-value. Always. No exceptions.

If Ruby were pass-by-reference, this would print Ruby is pass-by-reference.

Answer 3

Yes

Both method calls will take about the same amount of time.

(It's good to be aware of performance consequences and you asked a reasonable question, but even so, the standard disclaimer¹ about early optimization technically applies.)

---

^{1. First, make program work. Then, profile. Finally, and maybe, optimize.
Donald Knuth said: We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.}

Answer 4

For example, I would go with the _id variant. I prefer to always be able to get the correct state of my objects. It's never fun to work with stale ones.

Answer 5

Well everything is an Object in ruby (everything inherits from Object) and ruby always passes objects by ref so both of your examples are passing by reference!