obj.nil? vs. obj == nil
Is it better to use obj.nil? or obj == nil and what are the benefits of both?
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Syntax and style aside, I wanted to see how "the same" various approaches to testing for nil were. So, I wrote some benchmarks to see, and threw various forms of nil testing at it.
TL;DR - Results First
The actual results showed that using
objas a nil check is the fastest in all cases.objis consistently faster by 30% or more than checkingobj.nil?.Surprisingly,
objperforms about 3-4 times as fast as variations onobj == nil, for which there seems to be a punishing performance penalty.Want to speed up your performance-intensive algorithm by 200%-300%? Convert all
obj == nilchecks toobj. Want to sandbag your code's performance? Useobj == nileverywhere that you can. (just kidding: don't sandbag your code!).In the final analysis, always use
obj. That jives with the Ruby Style Guide rule: Don't do explicit non-nil checks unless you're dealing with boolean values.The Benchmark Conditions
OK, those are the results. So how is this benchmark put together, what tests were done, and what are the details of the results?
The nil checks that I came up with are:
objobj.nil?!obj!!objobj == nilobj != nil
I picked various Ruby types to test, in case the results changed based on the type. These types were
Fixnum,Float,FalseClass,TrueClass,String, andRegex.I used these nil check conditions on each of the types to see if there was a difference between them, performance-wise. For each type, I tested both nil objects and non-nil value objects (e.g.
1_000_000,100_000.0,false,true,"string", and/\w/) to see if there's a difference in checking for nil on an object that is nil versus on an object that's not nil.The Benchmarks
With all of that out of the way, here is the benchmark code:
require 'benchmark' nil_obj = nil N = 10_000_000 puts RUBY_DESCRIPTION [1_000_000, 100_000.0, false, true, "string", /\w/].each do |obj| title = "#{obj} (#{obj.class.name})" puts "============================================================" puts "Running tests for obj = #{title}" Benchmark.bm(15, title) do |x| implicit_obj_report = x.report("obj:") { N.times { obj } } implicit_nil_report = x.report("nil_obj:") { N.times { nil_obj } } explicit_obj_report = x.report("obj.nil?:") { N.times { obj.nil? } } explicit_nil_report = x.report("nil_obj.nil?:") { N.times { nil_obj.nil? } } not_obj_report = x.report("!obj:") { N.times { !obj } } not_nil_report = x.report("!nil_obj:") { N.times { !nil_obj } } not_not_obj_report = x.report("!!obj:") { N.times { !!obj } } not_not_nil_report = x.report("!!nil_obj:") { N.times { !!nil_obj } } equals_obj_report = x.report("obj == nil:") { N.times { obj == nil } } equals_nil_report = x.report("nil_obj == nil:") { N.times { nil_obj == nil } } not_equals_obj_report = x.report("obj != nil:") { N.times { obj != nil } } not_equals_nil_report = x.report("nil_obj != nil:") { N.times { nil_obj != nil } } end endThe Results
The results were interesting, because Fixnum, Float, and String types performance was virtually identical, Regex nearly so, and FalseClass and TrueClass performed much more quickly. Testing was done on MRI versions 1.9.3, 2.0.0, 2.1.5, and 2.2.5 with very similar comparative results across the versions. The results from the MRI 2.2.5 version are shown here (and available in the gist:
ruby 2.2.5p319 (2016-04-26 revision 54774) [x86_64-darwin14] ============================================================ Running tests for obj = 1000000 (Fixnum) user system total real obj: 0.970000 0.000000 0.970000 ( 0.987204) nil_obj: 0.980000 0.010000 0.990000 ( 0.980796) obj.nil?: 1.250000 0.000000 1.250000 ( 1.268564) nil_obj.nil?: 1.280000 0.000000 1.280000 ( 1.287800) !obj: 1.050000 0.000000 1.050000 ( 1.064061) !nil_obj: 1.070000 0.000000 1.070000 ( 1.170393) !!obj: 1.110000 0.000000 1.110000 ( 1.122204) !!nil_obj: 1.120000 0.000000 1.120000 ( 1.147679) obj == nil: 2.110000 0.000000 2.110000 ( 2.137807) nil_obj == nil: 1.150000 0.000000 1.150000 ( 1.158301) obj != nil: 2.980000 0.010000 2.990000 ( 3.041131) nil_obj != nil: 1.170000 0.000000 1.170000 ( 1.203015) ============================================================ Running tests for obj = 100000.0 (Float) user system total real obj: 0.940000 0.000000 0.940000 ( 0.947136) nil_obj: 0.950000 0.000000 0.950000 ( 0.986488) obj.nil?: 1.260000 0.000000 1.260000 ( 1.264953) nil_obj.nil?: 1.280000 0.000000 1.280000 ( 1.306817) !obj: 1.050000 0.000000 1.050000 ( 1.058924) !nil_obj: 1.070000 0.000000 1.070000 ( 1.096747) !!obj: 1.100000 0.000000 1.100000 ( 1.105708) !!nil_obj: 1.120000 0.010000 1.130000 ( 1.132248) obj == nil: 2.140000 0.000000 2.140000 ( 2.159595) nil_obj == nil: 1.130000 0.000000 1.130000 ( 1.151257) obj != nil: 3.010000 0.000000 3.010000 ( 3.042263) nil_obj != nil: 1.170000 0.000000 1.170000 ( 1.189145) ============================================================ Running tests for obj = false (FalseClass) user system total real obj: 0.930000 0.000000 0.930000 ( 0.933712) nil_obj: 0.950000 0.000000 0.950000 ( 0.973776) obj.nil?: 1.250000 0.000000 1.250000 ( 1.340943) nil_obj.nil?: 1.270000 0.010000 1.280000 ( 1.282267) !obj: 1.030000 0.000000 1.030000 ( 1.039532) !nil_obj: 1.060000 0.000000 1.060000 ( 1.068765) !!obj: 1.100000 0.000000 1.100000 ( 1.111930) !!nil_obj: 1.110000 0.000000 1.110000 ( 1.115355) obj == nil: 1.110000 0.000000 1.110000 ( 1.121403) nil_obj == nil: 1.100000 0.000000 1.100000 ( 1.114550) obj != nil: 1.190000 0.000000 1.190000 ( 1.207389) nil_obj != nil: 1.140000 0.000000 1.140000 ( 1.181232) ============================================================ Running tests for obj = true (TrueClass) user system total real obj: 0.960000 0.000000 0.960000 ( 0.964583) nil_obj: 0.970000 0.000000 0.970000 ( 0.977366) obj.nil?: 1.260000 0.000000 1.260000 ( 1.265229) nil_obj.nil?: 1.270000 0.010000 1.280000 ( 1.283342) !obj: 1.040000 0.000000 1.040000 ( 1.059689) !nil_obj: 1.070000 0.000000 1.070000 ( 1.068290) !!obj: 1.120000 0.000000 1.120000 ( 1.154803) !!nil_obj: 1.130000 0.000000 1.130000 ( 1.155932) obj == nil: 1.100000 0.000000 1.100000 ( 1.102394) nil_obj == nil: 1.130000 0.000000 1.130000 ( 1.160324) obj != nil: 1.190000 0.000000 1.190000 ( 1.202544) nil_obj != nil: 1.200000 0.000000 1.200000 ( 1.200812) ============================================================ Running tests for obj = string (String) user system total real obj: 0.940000 0.000000 0.940000 ( 0.953357) nil_obj: 0.960000 0.000000 0.960000 ( 0.962029) obj.nil?: 1.290000 0.010000 1.300000 ( 1.306233) nil_obj.nil?: 1.240000 0.000000 1.240000 ( 1.243312) !obj: 1.030000 0.000000 1.030000 ( 1.046630) !nil_obj: 1.060000 0.000000 1.060000 ( 1.123925) !!obj: 1.130000 0.000000 1.130000 ( 1.144168) !!nil_obj: 1.130000 0.000000 1.130000 ( 1.147330) obj == nil: 2.320000 0.000000 2.320000 ( 2.341705) nil_obj == nil: 1.100000 0.000000 1.100000 ( 1.118905) obj != nil: 3.040000 0.010000 3.050000 ( 3.057040) nil_obj != nil: 1.150000 0.000000 1.150000 ( 1.162085) ============================================================ Running tests for obj = (?-mix:\w) (Regexp) user system total real obj: 0.930000 0.000000 0.930000 ( 0.939815) nil_obj: 0.960000 0.000000 0.960000 ( 0.961852) obj.nil?: 1.270000 0.000000 1.270000 ( 1.284321) nil_obj.nil?: 1.260000 0.000000 1.260000 ( 1.275042) !obj: 1.040000 0.000000 1.040000 ( 1.042543) !nil_obj: 1.040000 0.000000 1.040000 ( 1.047280) !!obj: 1.120000 0.000000 1.120000 ( 1.128137) !!nil_obj: 1.130000 0.000000 1.130000 ( 1.138988) obj == nil: 1.520000 0.010000 1.530000 ( 1.529547) nil_obj == nil: 1.110000 0.000000 1.110000 ( 1.125693) obj != nil: 2.210000 0.000000 2.210000 ( 2.226783) nil_obj != nil: 1.170000 0.000000 1.170000 ( 1.169347)
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