From: Joel VanderWerf <vjoel@...>
Date: 2007-05-31T10:56:54+09:00
Subject: Re: `concat': can't modify frozen string in benchmark.rb

Pe�a wrote:
> Hi All,
> 
> C:\family\ruby>cat test.rb
> def f(command_here)
>    `#{command_here}`
> end
> a  =  {  "Local copy"=>"copy test.txt test.txt2"  }
> require 'benchmark'
> Benchmark.bmbm do |x|
>    a.each do |k,v|
>       x.report(k) { f v }
>    end
> end
> 
> C:\family\ruby>ruby test.rb
> c:/ruby/lib/ruby/1.8/benchmark.rb:334:in `concat': can't modify frozen string (T
> ypeError)
>         from c:/ruby/lib/ruby/1.8/benchmark.rb:334:in `report'
>         from test.rb:12
>         from test.rb:11:in `each'
>         from test.rb:11
>         from c:/ruby/lib/ruby/1.8/benchmark.rb:250:in `bmbm'
>         from test.rb:10
> C:\family\ruby>
> 
> if i comment out line 334 in benchmark.rb like so,
> 
>      #label.concat ' '
> 
> It works.
> It also works for the ff cases
>    x.report(k) { f v }
>    x.report() { f v }
>    x.report("") { f v }
>    x.report("test") { f v }
> 
> What is the relevance of line 334 in benchmark.rb?
> If the line is important, how can I fix my program so I can pass a var in x.report?
> 
> thank you and kind regards -botp
> 

A quick workaround would be to use k.dup:

       x.report(k.dup) { f v }

Apparently, benchmark is being bad and munging its inputs (and falling 
down when one of them happens to be frozen because it is also a hash key).

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407