From: Pit Capitain <pit@...>
Date: 2001-12-25T18:27:25+09:00
Subject: [ruby-talk:29410] Re: a better way?

On 24 Dec 2001, at 3:57, Ron Jeffries wrote:

> On Sun, 23 Dec 2001 03:48:19 GMT, nobu.nokada@softhome.net wrote:
> 
> >  class Temp
> >    @@save = Hash.new do |h, c|
> >      puts "Performing calculation...."
> >      h[c] = c * 9 / 5 + 32
> >    end
> >    def fahrenheit(c)
> >      @@save[c]
> >    end
> >  end
> 
> These are way cool.  I gather the 1.7.2 feature is new? I think I'm in
> 1.6 and it doesn't work there. 


On 1.6.x, you still can use the ||= assignment operator:

class Temp
  @@save = {}
  def fahrenheit(c)
    @@save[c] ||= begin
      print "calculating... "
      c * 9 / 5 + 32
    end
  end
end

t = Temp.new

puts t.fahrenheit(100)  # calculating... 212
puts t.fahrenheit(100)  # 212
puts t.fahrenheit(300)  # calculating... 572

If you omit the print statement, you even get the one-liner you 
originally wanted:

class Temp
  @@save = {}
  def fahrenheit(c)
    @@save[c] ||= c * 9 / 5 + 32
  end
end

t = Temp.new

puts t.fahrenheit(100)  # 212
puts t.fahrenheit(100)  # 212
puts t.fahrenheit(300)  # 572

Merry Christmas everybody,
Pit