From: Eric Hodel <drbrain@...7.net>
Date: 2005-01-19T09:29:37+09:00
Subject: Re: is defined? fast?

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On 18 Jan 2005, at 15:24, Mark Hubbart wrote:

> On Mon, 17 Jan 2005 22:26:17 +0900, George  Moschovitis
> <george.moschovitis@gmail.com> wrote:
>> Hello everyone, I have a simple question:
>>
>> is 'if defined?(MyFlag)' as fast as 'if $my_flag'
>> or is it much slower?
>
> A quick check suggests that defined? *might* be just slightly slower.
> But probably not enough to matter. You may want to profile your
> scripts (just "require 'profile'" at the top) and see what's best in
> your case.

No, profile cannot detect a global test or defined? being called, 
because they are not method calls.  You want to use benchmark.rb.

defined? MyFlag is at best almost half as fast as $my_flag, probably 
because defined? does not just return true (it returns a String).

$ cat x.rb
require 'benchmark'

TIMES = ARGV.shift || 100_000
$x = true
@x = true
@@x = true

module X; X = true; end

Benchmark.benchmark do |bm|
   bm.report "baseline                 " do
   end

   bm.report "defined? Nested::Constant" do
     TIMES.times do
       true if defined? X::X
       true if defined? X::Y
     end
   end

   bm.report "defined? Constant        " do
     TIMES.times do
       true if defined? Benchmark
       true if defined? NoSuchConst
     end
   end

   bm.report "defined? $global         " do
     TIMES.times do
       true if defined? $x
       true if defined? $y
     end
   end

   bm.report "defined? local           " do
     TIMES.times do
       true if defined? bm
       true if defined? no_such_local
     end
   end

   bm.report "defined? @var            " do
     TIMES.times do
       true if defined? @x
       true if defined? @no_such_ivar
     end
   end

   bm.report "defined? @@var           " do
     TIMES.times do
       true if defined? @@x
       true if defined? @@no_such_cvar
     end
   end

   bm.report "$global                  " do
     TIMES.times do
       true if $x
       true if $y
     end
   end
end

$ ruby x.rb
baseline                   0.000000   0.000000   0.000000 (  0.000046)
defined? Nested::Constant  0.680000   0.000000   0.680000 (  0.884762)
defined? Constant          0.370000   0.000000   0.370000 (  0.458034)
defined? $global           0.320000   0.000000   0.320000 (  0.336950)
defined? local             0.330000   0.000000   0.330000 (  0.345521)
defined? @var              0.370000   0.000000   0.370000 (  0.455369)
defined? @@var             0.370000   0.000000   0.370000 (  0.400793)
$global                    0.150000   0.000000   0.150000 (  0.174302)

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
FEC2 57F1 D465 EB15 5D6E  7C11 332A 551C 796C 9F04

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