From: Robert Klemme <bob.news@...>
Date: 2004-10-20T22:14:30+09:00
Subject: Re: Too many default argument values!


"Matt Maycock" <ummaycoc@gmail.com> schrieb im Newsbeitrag
news:e86cebfb04102005431b958b4f@mail.gmail.com...
> Putting everything in a default hash is sort of a bad idea.
>
> ------------------------- code -------------------------
> [ummaycoc@localhost ummaycoc]$ ruby -e '
> DEFAULT_ARGS = {:foo => :meow, :santa => :love}.freeze
> puts("-" * 50)
> p DEFAULT_ARGS
> def test(arg1, opt_args=DEFAULT_ARGS)
>   puts "Test: #{opt_args.inspect}"
> end
>
> puts
> test(:hey)
> puts
> test(:two, :foo => 1, :ruby => :language)'
> --------------------------------------------------
> {:santa=>:love, :foo=>:meow}
>
> Test: {:santa=>:love, :foo=>:meow}
>
> Test: {:ruby=>:language, :foo=>1}
> ------------------------- end code -------------------------
>
> Actually using it, you lose the fact that santa maps to love (thus
> everything in the `optional' hash is `mandatory')
>
> a much better idea would be:
>
> DEFAULT_HASH = { ... }
> def myFunc(arg1, ..., argN, optHash={})
>   DEFAULT_HASH.keys.each {|k|
>     optHash[k] = DEFAULT_HASH[k] unless optHash.include?(k)
>   }
>   ....
> end
>
>
> This gives you what you actually want.  I hope.

True.  I forgot that.  Alternatives:

DEFAULT_HASH = { ... }.freeze
def myFunc(a, b, args={})
  @a = a
  @b = b
  @foo = args[:foo] || DEFAULT_HASH[:foo]
  ....
end

or

DEFAULT_HASH = { ... }.freeze

def rect(a, b, args = DEFAULT_HASH)
  tmp = DEFAULT_HASH.dup.update( args )
  ...
  @a = a
  @b = b
  @foo = tmp[:foo]
  ...
end

Kind regards

    robert

>
>
> On Wed, 20 Oct 2004 18:24:24 +0900, Robert Klemme <bob.news@gmx.net>
wrote:
> >
> > "Tim Hunter" <cyclists@nc.rr.com> schrieb im Newsbeitrag
> > news:j%gdd.27795$zA3.4433422@twister.southeast.rr.com...
> > > Looking for coding style advice...
> > >
> > > I'm trying to write a method that describes a rectangle. A rectangle
is
> > > defined by the x,y coordinates of its upper-left corner and its
width
> > and
> > > height. These values are required. Optionally, the rectangle can
have
> > > "styles," like the fill color and the stroke color. Also optionally,
the
> > > rectangle can have rounded corners, if you specify how much rounding
you
> > > want in the x and y directions. (The default is square corners.)
> > >
> > > The method I started with is:
> > >
> > > def rect(x, y, width, height, rx=0, ry=0, styles=nil)
> > >         # blah, blah, blah
> > > end
> > >
> > > Where the styles argument (if present) is a Hash formed by the usual
> > > trailing key=>value pairs. All very standard Ruby.
> > >
> > > I was thinking that you'd create a square-corner rectangle like
this:
> > >
> > > canvas.rect(10, 10, 20, 30, :fill=>'black', :stroke='red')
> > >
> > > But of course that doesn't work, because the styles hash
> > > "{:fill=>'black', :stroke=>'red'}" gets assigned to rx, not to
styles.
> > >
> > > Of course, within rect I could test the class of rx and/or ry and if
> > it's a
> > > Hash, assign it to styles, but that seems kludgy and insufficiently
> > > Rubyish. I could divide rect into two methods, rect and
rounded_rect,
> > but
> > > that means that the user has to remember an extra method name. I
could
> > make
> > > rx and ry required arguments. Blech.
> > >
> > > Thoughts?
> >
> > Put all (optional) args into the hash and use a default hash
> >
> > def rect(x, y, width, height, args={:rx=>0, :ry=>0})
> >         # blah, blah, blah
> >   p x
> >   p y
> >   p width
> >   p height
> >   p args
> > end
> >
> > Alternative with slightly better performance:
> >
> > DEFAULT_RECT_ARGS = {
> >   :rx => 0,
> >   :ry => 0,
> > }.freeze
> >
> > def rect(x, y, width, height, args=DEFAULT_RECT_ARGS)
> > ....
> >
> > >> rect(10, 10, 20, 30, :fill=>'black', :stroke=>'red')
> > 10
> > 10
> > 20
> > 30
> > {:stroke=>"red", :fill=>"black"}
> >
> > or even
> >
> > def rect(args=DEFAULT_RECT_ARGS)
> > ....
> >
> > Kind regards
> >
> >     robert
> >
> >
>
>
> -- 
> There's no word in the English language for what you do to a dead
> thing to make it stop chasing you.
>
>