From: Justin Collins <justincollins@...>
Date: 2008-07-30T04:46:55+09:00
Subject: Re: Interesting Array Initialization Typo

Dave Bass wrote:
> Regarding typos: Ruby can't be expected to know what you meant to type, 
> so if it's syntactically correct it will let it through -- as with any 
> language! To do otherwise would be as annoying as Microsoft's Clippy: "I 
> see you're trying to set up an array. Did you just make a typo? <wink>"
>
> Shadowfirebird wrote:
>   
>> a = []
>> a << [1,2]
>> a << [2,3]
>> a << [3,4]
>>     
>
> Without any actual understanding of what's going on inside Ruby 
> (sorry!), I suspect this code will be slower, as the array has to be 
> grown three times, rather than springing into existence fully 
> initialised. Or is this a negligible overhead? Or does the code get 
> optimised by the compiler/interpreter? Maybe someone knowledgeable would 
> like to comment.
>
> In particular it would be interesting to know if putting array pushes, 
> pops, shifts and unshifts inside a big loop is inefficient.
>
> Dave
>   

Here's what I got:

Rehearsal --------------------------------------
<<   0.990000   0.290000   1.280000 (  1.331386)
[]   0.060000   0.000000   0.060000 (  0.070595)
----------------------------- total: 1.340000sec

         user     system      total        real
<<   0.940000   0.320000   1.260000 (  1.302148)
[]   0.060000   0.010000   0.070000 (  0.070150)


With
ruby 1.8.6 (2008-03-03 patchlevel 114) [x86_64-linux-gnu]

and

require 'benchmark'
include Benchmark

bmbm do |t|
    t.report("<<") do
        10000.times do
            a = []
            100.times do |x|
                a << x
            end
        end
    end

    t.report("[]") do
        10000.times do
            a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 
16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 
34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 
70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 
88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
        end
    end
end


-Justin