From: Robert Klemme <shortcutter@...>
Date: 2007-07-20T18:33:42+09:00
Subject: Re: syntactic sugar buzz

2007/7/19, Sam Smoot <ssmoot@gmail.com>:
> On Jul 17, 8:52 pm, Jeff Pritchard <j...@jeffpritchard.com> wrote:
> > I'm a relative newbie.  I'm finally getting the hang of some of the
> > syntactic sugar provided, such as the whole thing about using the "or"
> > operator to provide a default value if something is nil:
> >
> > foo = bar || "emptiness"
> >
> > One thing I keep running into over and over and over and over that I
> > wish there was some syntactic sugar for is the whole business of calling
> > a method on an object, and doing something intelligent if the object is
> > nil.
> >
> > If I have a string of stuff like:
> > blah = foo.bar.split
> >
> > what if bar is nil?  There are obvious long hand ways to deal with this,
> > but then you loose the smoothness of lining up things like this in Ruby.
> >
> > I guess what I want is some syntactic sugar that means "this object, or
> > an empty one of these if this is nil", so that I would get an empty
> > result instead of a nil object missing method error.
> >
> > I would like to be able to write:
> > blah = foo.bar||empty(bar).split
> >
> > This could be written:
> > blah = foo.bar||"".split
> >
> > But that requires a well known object type for bar.  What if it is:
> > blah = foo.bar.whatchamacallit()
> >
> > where bar is some oddball object of your own imagining.
> >
> > Have you veteran Rubyists come up with a nice way to write stuff like
> > this that keeps the nice clean flow of Ruby's chaining in place, but
> > solves the problems with potentially nil intermediate results?
> >
> > thanks,
> > jp
> >
> > --
> > Posted viahttp://www.ruby-forum.com/.
>
> It feels like it could be shortened, perhaps the :type is unnecessary,
> but I was thinking of something like this for my DataMapper to ease
> the pain of using object graphs in simple tabular reporting views...
>
>   class Object
>     def default(type)
>       self || type.new
>     end
>   end
>
>   class Person
>     attr_accessor :name
>     def initialize(name)
>       @name = name
>     end
>   end
>
>   people = [ Person.new('Bob'), nil ]
>
>   for person in people
>     puts "Hello " + person.default(Person).name
>   end

I think you can save more typing if you default the type parameter to
self.class. Then you have

puts "Hello " + person.default.name

> Which isn't _too_ ugly I think. On the other hand you could end up
> with something like this:
>
>   puts @photo.default(Article).article.default(Category).category.name
>
> Instead of:
>
>   puts @photo.article.category.name
>
> But that's obviously more than a bit contrived. Any ideas would be
> welcome though...

Hm...  One thing I do not like about this is that there has to be a
new object created for every "missing" instance.  I'd do your sample
differently: either remove nils from the array beforehand or add a "
if person" at the end of the "puts" statement.

Kind regards

robert