From: Joey Zhou <yimutang@...>
Date: 2011-03-09T12:45:04+09:00
Subject: Unexpected problem: hash[key] << value

# ruby 1.9.2p180 (2011-02-18) [i386-mingw32]

get_page_hash = {}
get_page_hash.default = []

File.foreach("page.txt") do |line|
  word, page = line.chomp.split(':')
  get_page_hash[word] << page # the problem is here
end

p get_page_hash['Aword'] # => ["1", "2", "3", "4", "5"]
p get_page_hash['Bword'] # => ["1", "2", "3", "4", "5"]
p get_page_hash.default  # => ["1", "2", "3", "4", "5"]

__END__

content of page.txt:
Aword:1
Bword:2
Cword:3
Aword:4
Dword:5


Simple program, clear purpose. I don't know why get_page_hash.default
becomes ["1", "2", "3", "4", "5"], it seems radiculous.

Only if I modify the very line to:

  get_page_hash[word] += [page]

I get what I want:

p get_page_hash['Aword'] # => ["1", "4"]
p get_page_hash['Bword'] # => ["2"]
p get_page_hash.default  # => []

I think use "<<" maybe intuitive, but the result is unexpected. What's
wrong with it?

Thank you!

Joey

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