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When to use .nil? in Ruby methods

The problem

Nil? is overused. I find myself deleting it a lot.

I stopped using nil? once I learned that:

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if person.nil?
  make_person
end

Has the same effect as

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unless person
  make_person
end

or

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make_person unless person

Thus, when I read code, it is equally clear to me what someone means when they use either one.

Given that, it strikes me as bulky whenever I see nil?, unless of course the person legitimately needs a bool, which is rare.

Another reason

Calling nil? also makes your code slower.

Contrived example

This is obviously a pretty contrived example, but check it out:

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require 'benchmark'

Benchmark.bm do|b|

b.report("without .nil?") do
  cat = nil
  bat = 'vampire'
  2_000_000.times do
    unless bat        
      true if cat
    end
  end
end


b.report("with nil? ") do
  cat = nil
  bat = 'vampire'
  2_000_000.times do
    unless bat.nil?
      true unless cat.nil?        
    end
  end
end

end

Results user system total
without .nil? 0.290000 0.000000 0.290000 ( 0.298643)
with nil? 0.780000 0.000000 0.780000 ( 0.788894)

So, without nil? is, at least in this not at all scientific test, more than twice as slow. In Ruby, we tend to not care about speed, by why gimp yourself on purpose? Especially when the faster way is equally, if not more, clear?

When to use nil? in Ruby methods? Imo never.

May 21, 2009

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