Ruby question - == nil or nil? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

obj.nil? vs. obj ==开发者_如何学JAVA nil

I found a question - which one is better == nil or nil?

I always thought that these 2 things do the same. Is there any difference?

---

There is one difference: A class may define nil? as true:

class X
  def nil?()
    true
  end
end

puts X.new.nil? #-> true

Or a practical example (i don't recommend it, if you need it, I would define a nil_or_empty?):

class String
  def nil?()
    return empty?
  end
end

puts 'aa'.nil? #-> false
puts ''.nil? #-> true

---

Running a benchmark nil? seems to be a bit faster.

require 'benchmark'

TEST_LOOPS = 100_000_000

C_A = nil
C_B = 'aa'

Benchmark.bmbm(10) {|b|

  b.report('nil?') {
   TEST_LOOPS.times { 
      x = C_A.nil?
      x = C_B.nil?
   }            #Testloops
  }
  b.report('==nil') {
   TEST_LOOPS.times { 
      x = ( C_A == nil )
      x = ( C_B == nil )
   }            #Testloops
  }             #b.report

} #Benchmark

Result:

Rehearsal ---------------------------------------------
nil?       27.454000   0.000000  27.454000 ( 27.531250)
==nil      31.000000   0.000000  31.000000 ( 31.078125)
----------------------------------- total: 58.454000sec

                user     system      total        real
nil?       27.515000   0.000000  27.515000 ( 27.546875)
==nil      31.125000   0.000000  31.125000 ( 31.171875)

---

Although the two operations are very different I'm pretty sure they will always produce the same result. (One calls the #nil? method of a NilClass object and one compares against the nil singleton.)

I would suggest that when in doubt you go a third way, actually, and just test the truth value of an expression.

So, if x and not if x == nil or if x.nil?, in order to have this test DTRT when the expression value is false.