Forum: Ruby on Rails Regarding the design of ActiveSupport::TimeZone

889cf720c96957e615463b5c903a5e18?d=identicon&s=25 Matt Johnson (Guest)
on 2013-08-22 10:58
(Received via mailing list)
Hello,  I am relatively new to RoR, but vastly experienced with time
zones
and date/time issues on other multiple other platforms.

I answer quite a few questions on StackOverflow in this area, and often
questions about ActiveSupport::TimeZone come up.  I'm hoping that
someone
from this forum can provide the background behind this implementation,
such
that I am better informed to address these questions.

My understanding is that the Ruby TZInfo gem is the base implementation
of
the IANA/Olson time zone database, but Rails ships with
ActiveSupport::TimeZone which is based on this, with some changes.  It's
the changes that I'm unsure about.

From the documentation here:
http://api.rubyonrails.org/classes/ActiveSupport/T...

> The TimeZone<http://api.rubyonrails.org/classes/ActiveSupport/T...
class
serves as a wrapper around TZInfo::Timezone instances.

This is the basis for my earlier statements.  But, WHY was it created?
Why
not just use the TZInfo gem?

>  It allows us to do the following:
>    Limit the set of zones provided by TZInfo to a meaningful subset of
146 zones.

Ok - but who determined which of the 578 zones are "meaningful"?  By
what
criteria?  And by what review process do newly established zones get
determined if they make the cut or not? Is there a recommended strategy
for
dealing with zones that were omitted?
Also, why limit it to begin with?  The size of the database shouldn't be
an
issue - since this is all server-side code.  I could see perhaps
providing
a method to retrieve those that are "meaningful" from the larger data
set,
but it doesn't make sense to me that they are omitted.


> Retrieve and display zones with a friendlier name (e.g., Eastern
Time<http://api.rubyonrails.org/classes/Time.html>
 (US & Canada) instead of America/New_York).

Again, who decides what "friendlier" means?  I sure hope the original
names
are not lost - since those are keys used for interoperability with other
systems that also implement the TZDB.  Are they still available on the
TimeZone object?  What about non-English speakers, are these names
localized for them?  Some of the names are quite reminiscent of the
Display
Names of the proprietary Microsoft Windows time zones. Did that have an
influence on their creation?

I see that the MAPPING constant is available in the documentation.  That
is
good.  I haven't fully digested it though - is it a one-to-one mapping?
 Does it handle TZDB link alias, such as Asia/Calcutta => Asia/Kolkata
or
US/Eastern => America/New_York ?

Thank you in advance for any and all information that you can provide.

-Matt Johnson
81b61875e41eaa58887543635d556fca?d=identicon&s=25 Frederick Cheung (Guest)
on 2013-08-23 10:44
(Received via mailing list)
On Thursday, August 22, 2013 12:59:02 AM UTC+1, Matt Johnson wrote:
>
>

> > Retrieve and display zones with a friendlier name (e.g., Eastern
Time<http://api.rubyonrails.org/classes/Time.html>
>  (US & Canada) instead of America/New_York).
>
>
It may not be a size issue server side, but since part of what this does
is
power the time_zone_options_for_select form helper, there may have been
user friendllyness concerns - all other things being equal a drop down
with
146 options is friendlier than one with 500 options. People on the east
coast (I assume) identifiy with Eastern Time (US & Canada) but someone
in
Montreal or Miami might not instantly realise that they need to pick
America/New_York.

I think this is also partly an accident of history. Early versions of
rails
didn't wrap the tzinfo gem (in fact they predate the gem) - I assumed
some
backwards compatiblity concerns came into play when it was refactored to
be
based on tzinfo


> Again, who decides what "friendlier" means?  I sure hope the original
> names are not lost - since those are keys used for interoperability with
> other systems that also implement the TZDB.  Are they still available on
> the TimeZone object?  What about non-English speakers, are these names
> localized for them?  Some of the names are quite reminiscent of the
> Display Names of the proprietary Microsoft Windows time zones. Did that
> have an influence on their creation?
>
> You can access the underlying tzinfo object.


> I see that the MAPPING constant is available in the documentation.  That
> is good.  I haven't fully digested it though - is it a one-to-one mapping?
>  Does it handle TZDB link alias, such as Asia/Calcutta => Asia/Kolkata or
> US/Eastern => America/New_York ?
>
> Don't know. You may also find the rubyonrails-core list helpful or the
rails-contrib IRC channel -

Fred
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