From: Brian Candler <b.candler@...>
Date: 2009-02-03T22:04:43+09:00
Subject: Re: choose parameter to solve for

Jason Lillywhite wrote:
> class Foo
>   def initialize(x, y, z)
>     @x, @y, @z = x, y, z
>   end
> 
>   def function(var)
>     if @x.nil?
>       @x = var
>     elsif @y.nil?
>       @y = var
>     else
>       @z = var
>     end
>     @x + @y + @z
>   end
> 
> end
> 
> z = Foo.new(1, 2, nil)
> z.function(3)
> => 6

Also, if this is really the pattern you want (an object holding default 
values for each of the args), then you probably don't want to modify the 
instance variables between invocations. So here is a more general 
version:

class Foo
  def initialize(*args)
    @args = args
  end
  def function(*more)
    # for each nil argument, pick one from 'more'
    calculate(*@args.collect { |x| x || more.shift })
  end
  def calculate(x,y,z)
    x + y + z
  end
end
z = Foo.new(1,2,nil)
z.function(3)
q = Foo.new(nil,nil,6)
q.function(4,5)

But I still think some flavour of currying is what you want. Is it 
important that arbitrary parameters are fixed, rather than just the 
left-most ones?
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