Finding last date

[Dipesh Batheja]

Hi,
Is there any instance method in Ruby for Date type, to find previous
date. For example if I have date - "04/05/07" in an object "date", then
something like "date.previous" returns me date - "04/04/07".

 

[Robert Klemme]

Hi,
Is there any instance method in Ruby for Date type, to find previous
date. For example if I have date - "04/05/07" in an object "date", then
something like "date.previous" returns me date - "04/04/07".

$ irb -r date
irb(main):002:0> Date.today.to_s
=> "2007-04-06"
irb(main):003:0> (Date.today - 1).to_s
=> "2007-04-05"
irb(main):004:0>

robert

 

[Jeremy Hinegardner]

Hi,
Is there any instance method in Ruby for Date type, to find previous
date. For example if I have date - "04/05/07" in an object "date", then
something like "date.previous" returns me date - "04/04/07".

The Date object can inherently do date arithmetic:

irb(main):001:0> require 'date'
irb(main):002:0> today = Date.today
irb(main):003:0> yesterday = today - 1
irb(main):004:0> puts "Today : #{today}"
Today : 2007-04-06
irb(main):006:0> puts "Yesterday : #{yesterday}"
Yesterday : 2007-04-05

So if you would like a today.prev then you can easily add #prev.
Date#succ already exists.

class Date
def prev
self - 1
end
end

If you want even more interesting time/date utility functions add in the
facets gem and try out the 'more/times' items, you can do things like
1.week.ago and 3.hours.from_now.

http://facets.rubyforge.org/src/doc/rdoc/more/classes/Numeric.html

enjoy,

-jeremy

 

[Dipesh Batheja]

Cool, thanks, thats great info.

 

[srinsriram]

On 06.04.2007 11:00, Dipesh Batheja wrote:> Hi,

$ irb -r date
irb(main):002:0> Date.today.to_s
=> "2007-04-06"
irb(main):003:0> (Date.today - 1).to_s
=> "2007-04-05"
irb(main):004:0>

robert

I just noticed that whitespace near the -1 makes a difference in the
evaluation in irb. is this expected?

irb(main):006:0> (Date.today -1).to_s
=> "2007-04-06"

irb(main):008:0> (Date.today - 1).to_s
=> "2007-04-05"

 

[Sam Smoot]

I just noticed that whitespace near the -1 makes a difference in the
evaluation in irb. is this expected?

irb(main):006:0> (Date.today -1).to_s
=> "2007-04-06"

irb(main):008:0> (Date.today - 1).to_s
=> "2007-04-05"

Yes. "-1" is "negative one", "- 1" is "minus one". So the former is
interpreted as passing the value -1 to the method
Date::today(sg=ITALY), while the latter is interpreted as calling
Date#- on the instance returned from Date::today and passing 1 as the
parameter to Date#-.

So it just goes to show, spacing matters, so better to be clear than
invalid.

If you think about it, if the left-hand-side contains a ".", so a
method call, the language parser can't interpret what you mean in this
example without giving significance to the whitespace.

If you try the same without a trailing method on the LHS, for example
"1 -1", then just like in math, the meaning becomes unambiguos, since
without interpreting the minus symbol as a call to Fixnum#-, there is
no expression, and the line would otherwise just be a syntax error.

So the parser is forgiving when it can be I suppose. Me, I prefer to
just use whitespace always unless I mean to actually represent a
negative number. To do otherwise just feels sloppy to me.

 

[Ken Bloom]

I just noticed that whitespace near the -1 makes a difference in the
evaluation in irb. is this expected?

irb(main):006:0> (Date.today -1).to_s => "2007-04-06"

irb(main):008:0> (Date.today - 1).to_s => "2007-04-05"

Yeah. The first way passes the value -1 as a parameter to Date.today.
The second way does math.

Ruby has lots of ambiguous operators like that (<< versus <<HEREDOC for
example), your best strategy is to always put whitespace around your
binary operators.

--Ken

 

[Bertram Scharpf]

Hi,

Am Freitag, 06. Apr 2007, 21:45:43 +0900 schrieb Jeremy Hinegardner:

On Fri, Apr 06, 2007 at 06:00:50PM +0900, Dipesh Batheja wrote:
If you want even more interesting time/date utility functions add in the
facets gem and try out the 'more/times' items, you can do things like
1.week.ago and 3.hours.from_now.

http://facets.rubyforge.org/src/doc/rdoc/more/classes/Numeric.html

Very nice. But unfortunately a month is not alway 30 days
and a year not always 365.

Bertram