How to pass a parameter to a method that is also a parameter itself in Ruby?

Question

*Apologies if the question's wording is confusing. I didn't know exactly how to ask it.

How can I do something like this?

def track_time(function, input)
    beg = Time.now

    function(input)

    end = Time.now
    end - beg
end

And then pass it a function and a value for that function to use.

def double(value)
    value + value
end

p track_time(double, 5)

The goal is to create something repeatable so I can track how long different functions take to complete.

Three quality answers so far. Consider yourself fortunate. – Cary Swoveland Jun 04 '16 at 15:06 — Cary Swoveland, Jun 04 '16 at 15:06

kirlev · Accepted Answer · 2016-06-04T15:53:37.510

First you can not use 'end' as a variable name.

As for your question, I agree with Mladen Jablanovićyou that for this use case a block is better, but since you specifically asked about passing a method as a parameter to another method, you can use the 'send' method:

def track_time method, value
  begin_time = Time.now
  send method, value
  end_time = Time.now
  end_time - begin_time
end

def double(value)
    value + value
end

p trcak_time(:double, 5)

score 3 · Answer 2 · edited May 23 '17 at 10:29

3

Unfortunately, methods in Ruby are not first-class objects, so they can't be directly passed as arguments. You can pass a name of the method (usually passed as symbol) instead, as other answers suggest.

But the idiomatic way to achieve what you are aiming for are blocks:

def track_time
  start = Time.now

  yield

  finish = Time.now
  finish - start
end

track_time do
  double(5)
end
#=> 6.127e-06

edited May 23 '17 at 10:29

Community

1
1

answered Jun 04 '16 at 15:02

Mladen Jablanović

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Is this preferable in "Ruby style" over using the "send" method? – tim_xyz Jun 04 '16 at 15:46
1

I personally would favor this style, as Mladen mentioned it is idiomatic Ruby. You could always write a one liner ``track_time { double(5) }`` if it is not too long. Not to mention, what would you do if you needed multiple arguments in another method? (sure you could use a splat operator but using a block seems the right way to go). – Nabeel Jun 04 '16 at 16:15
1

@pandaman `send` is primarily used to invoke methods dynamically, i.e. when you don't know in advance which method you need to invoke - for example, if actual method depends on user's input. Also, with block approach, you can measure duration of arbitrary code sequence, not only a single method call. – Mladen Jablanović Jun 04 '16 at 17:43

score 2 · Answer 3 · answered Jun 04 '16 at 14:56

Remember that end is a reserved word in Ruby (I suspect it was for illustration purposes anyhow).

You could pass in the string/symbol of the function name instead.

def track_time(function, input)
  start = Time.now

  method(function).call(input)

  finish = Time.now
  finish - start
end

def double(value)
  value + value
end

track_time('double', 5)
=> 6.127e-06

How to pass a parameter to a method that is also a parameter itself in Ruby?

3 Answers3