From: "Peña, Botp" <botp@...>
Date: 2008-08-08T18:59:38+09:00
Subject: Re: Most compact command for associate array 'totalling'?

From: Marc Heiler [mailto:shevegen@linuxmail.org] 
# I guess you have a point here, but visually I find the 
# shorter solution
#   a = Hash.new(0)
#   a['abc'] += 1
# more appealing.

careful, it's more than a face; the previous block example creates/assigns objects when called.

compare this,

irb(main):001:0> h=Hash.new 0
=> {}
irb(main):002:0> h[1]
=> 0
irb(main):003:0> h[2]
=> 0
irb(main):004:0> h
=> {}

w this,

irb(main):005:0> h=Hash.new{|h,k| h[k]=0}
=> {}
irb(main):006:0> h[1]
=> 0
irb(main):007:0> h[2]
=> 0
irb(main):008:0> h
=> {1=>0, 2=>0}

and this,

irb(main):011:0* h=Hash.new{|h,k| 0}
=> {}
irb(main):012:0> h[1]
=> 0
irb(main):013:0> h[2]
=> 0
irb(main):014:0> h
=> {}

(note that Hash.new{|h,k| 0} may evolve to Hash.new{0} or Hash.new(0); ie all of them do not assign/create to the hash)

the common denominator of the above is that they all do the ff (w same result)

irb(main):021:0> h[1] += 1
=> 1
irb(main):022:0> h
=> {1=>1}

So if you ask me, i find the hash block form very generic.

kind regards -botp (just another block fan :)