From: "Guy N. Hurst" <gnhurst@...>
Date: 2002-04-14T19:01:56+09:00
Subject: RCR: key value mapping for sprintf/%

I was on irc at irc.openprojects.net in #ruby-lang
last week when someone came in and asked if Ruby
had something like python's string formatting
templates. While we were able to refer him to
various templating/interpolating solutions, they
didn't solve his problem as directly as he expected.

After some discussion, we realized what he was asking.
Python allows you to pass a mapping (e.g. Hash) as
values to a format string.
(cf. http://www.python.org/doc/current/lib/typesseq-strings.html)

In Ruby, we have format strings, but they only accept a fixed
number of arguments, and are substituted in the order they are provided.

"This is first: %s, and this is 2nd: %s" % ['one','two']


But python allows something like this for the format string:

ftext = "%(name)s is %(gender)s. %(name)s is %(age)2d years old"


In Ruby, it might work like this:

hash = {'gender'=>"male", 'name'=>"Fred", 'age'=>23}
ftext % hash  # "Fred is male. Fred is 23 years old"


I wrote a substitute method for String#% which treats a Hash argument
as described above. It seems to be working fine, and I even posted
it to the RAA ("TextFormatTemplate").

However, it seems this is something that could (should?) be easily added
to Ruby itself. It would help those coming from Python, add a useful
feature, and be totally backwards-compatible. 

http://www.ruby-lang.org/en/raa-list.rhtml?name=TextFormatTemplate


Guy N. Hurst