From: Gary Wright <gwtmp01@...>
Date: 2008-02-29T08:20:08+09:00
Subject: Re: Named sprintf parameters


On Feb 28, 2008, at 11:57 AM, Trans wrote:
> I have a question and perhaps a bit of challenge for those with mad
> parse skills: Has anyone ever considered named parameters for sprintf/
> printf? It would be quite useful (to me at least) to be able to do:
>
>   "I am %(name)s." % { :name => "Tom" ]
>
> Has anyone worked on something like this before? Is there anything
> equivalent in the Perl world or other language?

I released a gem last year (http://jig.rubyforge.com) that defines
a data structure I nicknamed a Jig that enables this sort of thing
either by parsing a string to get the format or by explicit
construction:

j = Jig.new('I am ', :name)
j2 = Jig.parse('I am %{:name:}')

puts j % { :name => 'Tom'}       # I am Tom
puts j2 % { :name => 'Alice'}     # I am Alice

A Jig is a ordered sequence of objects and 'gaps'.  Simple gaps are
identified as symbols during Jig construction but you can also define
gaps that process anything that is used to fill them:

capitalize  = Jig::Gap.new(:name) { |x| x.capitalize }
j2 = Jig.new('before: ', :name, ' after: ', capitalize)
puts j2 % {:name => 'bob' }     # 'before: bob after: Bob'

In that example you can see that all gaps with the same name
are plugged simultaneously.  Unplugged gaps are rendered as
the empty string when Jig#to_s is called.

You can also construct a Jig or fill a gap with a proc/lambda/method
which will be evaluated at the time the Jig is rendered to a string:

    time = Jig.new("The time is ") {Time.now}
    puts time		# The time is Thu Feb 28 18:16:07 -0500 2008
    sleep 5
    puts time            # The time is Thu Feb 28 18:16:12 -0500 2008

The gem has classes for handling XML, XHTML, and CSS constructs.

I've made a few changes since the initialize release but haven't
gotten around to pushing it a new release to Rubyforge yet....

Gary Wright

http://jig.rubyforge.com