From: "David A. Black" <dblack@...>
Date: 2009-07-12T22:14:36+09:00
Subject: Re: A clean way to edit a time?

Hi --

On Sat, 11 Jul 2009, Max Williams wrote:

> Hi all
>
> I have a method, created_at=, which takes a time or a string, and
> changes a Time field, created_at, accordingly.  If we get a time, then
> it's easy: just set created_at to be the given time.
>
> However, if we get a string, it's going to be only a date, like
> "11/07/09", and in this case i want to update only the day, month and
> year of created_at, and leave the rest alone.  In some cases, like when
> a new record is made, then there will be no value in created_at, so the
> method should cope with the current value of created_at being nil (i do
> this by setting the time to Time.now before updating it with the new
> values).
>
> Currently i have this which feels like a bit of a hacky mess.  Can
> anyone show me a cleaner solution?
>
>
>    def created_at=(time)
>      if time.kind_of?(Time)
>        self[:created_at] = time
>      elsif time.kind_of?(String)
>        begin
>          parsed_time = DateTime.strptime(time, "%d/%m/%y")
>          old_time = self.created_at || Time.now
>          return self[:created_at] = Time.local(parsed_time.year,
> parsed_time.month, parsed_time.day, old_time.hour, old_time.min,
> old_time.sec)
>        rescue
>          return false
>        end
>      end
>    end
>
> Also, i can't get it to return the new time value, and it doesn't return
> false if it raises the exception.  In either case it just returns the
> string that i passed to it. It's not vital that it return the new
> created_at value (or false) but it would be nice.

To start with the last point: the setter methods are engineered to
look like and behave like assignments. So when you do this:

   obj.x = y

it always returns y. It's emulating assignment semantics:

   x = y   # always returns y

So using 'return' with an argument in those methods doesn't work.

As for your main question: I'm not sure whether this does exactly what
you want (though I've got some tests that suggest perhaps it does),
but here's a version that might at least give you some ideas:

require 'time'

class Thing
   attr_reader :created_at

   def created_at=(new_time)
     if new_time == new_time.to_s
       now = Time.now
       str = "#{new_time} #{now.strftime('%H:%M:%S')}"
       @created_at = Time.parse(str)
     else
       @created_at = new_time
     end
   end
end

The idea, as you can see, is to piece together a string that contains
the year, month, and day from the string that was passed in, plus the
hour, minute, and second from Time.now. I think it does what you want
with correct input, though some further checking for correctness might
be in order.


David

-- 
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Now available: The Well-Grounded Rubyist (http://manning.com/black2)
Training! Intro to Ruby, with Black & Kastner, September 14-17
(More info: http://rubyurl.com/vmzN)