From: Alex Gutteridge <alexg@...>
Date: 2007-10-22T10:36:23+09:00
Subject: Re: gsub does not work with do/end block, only brackets

On 22 Oct 2007, at 09:45, Michael Chow wrote:

> puts "abcdefg".gsub(/abc/) do |x|
>   x.upcase
> end
>
> ^This does not work. ArgumentError, it's expecting the second argument
> that's required when a block is not provided.
>
> puts "abcdefg".gsub(/abc/) { |x|
>   x.upcase
> }
>
> ^This works.
>
> Why??

It interprets the block you are trying to give to 'gsub' as a block  
argument to 'puts' instead. Brackets remove the ambiguity:

irb(main):008:0> "abc".gsub(/a/){|x| x.upcase}
=> "Abc"
irb(main):009:0> "abc".gsub(/a/) do |x| x.upcase end
=> "Abc"
irb(main):010:0> puts "abc".gsub(/a/){|x| x.upcase}
Abc
=> nil
irb(main):011:0> puts "abc".gsub(/a/) do |x| x.upcase end
ArgumentError: wrong number of arguments (1 for 2)
         from (irb):11:in `gsub'
         from (irb):11
irb(main):012:0> puts("abc".gsub(/a/) do |x| x.upcase end)
Abc
=> nil


Alex Gutteridge

Bioinformatics Center
Kyoto University