How to detect if variable has been defined yet?

ruby-talk
1

Hi,

I'd like to detect if a variable has been defined yet. Is this possible in Ruby or mod_ruby?

For example, I'd like to do the following:

if $total.exists
    $total = $total + 1
else
    $total = 0
end

2

defined? may be useful. Anyway, writing:

if variable
variable+=1
else
variable=0
end

should do just fine

···

il Fri, 02 Jul 2004 17:40:40 GMT, Randy Lawrence <jm@zzzzzzzzzzzz.com> ha scritto::

3

unless variable == nil has semantics.

-a

···

On Fri, 2 Jul 2004, gabriele renzi wrote:

il Fri, 02 Jul 2004 17:40:40 GMT, Randy Lawrence <jm@zzzzzzzzzzzz.com> > ha scritto::

defined? may be useful. Anyway, writing:

if variable
variable+=1
else
variable=0
end

should do just fine

--

EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
A flower falls, even though we love it;
and a weed grows, even though we do not love it. --Dogen

===============================================================================

4

if defined?($total)
    $total = $total + 1
else
    $total = 0
end

  Sean O'Dell

···

On Friday 02 July 2004 10:49, Randy Lawrence wrote:

Hi,

I'd like to detect if a variable has been defined yet. Is this possible
in Ruby or mod_ruby?

For example, I'd like to do the following:

if $total.exists
    $total = $total + 1
else
    $total = 0
end

5

Hi --

defined? may be useful. Anyway, writing:

if variable
variable+=1
else
variable=0
end

should do just fine

Have you tried it? :slight_smile:

$ ruby
if variable; variable += 1; else variable = 0; end
^D
-:1: undefined local variable or method `variable' for
main:Object (NameError)

I think you'd have to use defined?, or conditionally initialize the
variable:

  x ||= 0
  x += 1

(Note that you can't condense that into (x ||= 0) += 1, though you
could do: x = (x ||= 0) + 1 )

David

···

On Sat, 3 Jul 2004, gabriele renzi wrote:

il Fri, 02 Jul 2004 17:40:40 GMT, Randy Lawrence <jm@zzzzzzzzzzzz.com> > ha scritto::

--
David A. Black
dblack@wobblini.net

6

Sean O'Dell wrote:

···

On Friday 02 July 2004 10:49, Randy Lawrence wrote:

Hi,

I'd like to detect if a variable has been defined yet. Is this possible
in Ruby or mod_ruby?

For example, I'd like to do the following:

if $total.exists
   $total = $total + 1
else
   $total = 0
end

if defined?($total)
    $total = $total + 1
else
    $total = 0
end

  Sean O'Dell

Thanks! This was exactly what was needed and it works.

7

Actually to get what Randy wanted it would have to be:

  x ||= -1
  x += 1

or

  x = (x ||= -1) + 1

David

···

On Sat, 3 Jul 2004, David A. Black wrote:

I think you'd have to use defined?, or conditionally initialize the
variable:

  x ||= 0
  x += 1

--
David A. Black
dblack@wobblini.net

8

oops, sorry for disinforming :slight_smile:

···

il Sat, 3 Jul 2004 02:59:52 +0900, "David A. Black" <dblack@wobblini.net> ha scritto::

9

Use conditional assignment over defined?.

defined? is a sign of code smell. Variables should be explicitly
initialized before use.

···

David A. Black (dblack@wobblini.net) wrote:

Hi --

On Sat, 3 Jul 2004, gabriele renzi wrote:

> il Fri, 02 Jul 2004 17:40:40 GMT, Randy Lawrence <jm@zzzzzzzzzzzz.com> > > ha scritto::
>
>
> defined? may be useful. Anyway, writing:
>
> if variable
> variable+=1
> else
> variable=0
> end
>
> should do just fine
>

Have you tried it? :slight_smile:

$ ruby
if variable; variable += 1; else variable = 0; end
^D
-:1: undefined local variable or method `variable' for
main:Object (NameError)

I think you'd have to use defined?, or conditionally initialize the
variable:

  x ||= 0
  x += 1

(Note that you can't condense that into (x ||= 0) += 1, though you
could do: x = (x ||= 0) + 1 )

--
Eric Hodel - drbrain@segment7.net - http://segment7.net
All messages signed with fingerprint:
FEC2 57F1 D465 EB15 5D6E 7C11 332A 551C 796C 9F04

10

"David A. Black" <dblack@wobblini.net> writes:

  x ||= 0
  x += 1

(Note that you can't condense that into (x ||= 0) += 1, though you
could do: x = (x ||= 0) + 1 )

You can drop the inner assignment too:

  x = (x || 0) + 1

11

"Randy Lawrence" <jm@zzzzzzzzzzzz.com> schrieb im Newsbeitrag
news:JJhFc.31726$eH1.15066611@newssvr28.news.prodigy.com...

Sean O'Dell wrote:

>
>>Hi,
>>
>>I'd like to detect if a variable has been defined yet. Is this

possible

>>in Ruby or mod_ruby?
>>
>>For example, I'd like to do the following:
>>
>>if $total.exists
>> $total = $total + 1
>>else
>> $total = 0
>>end
>
>
> if defined?($total)
> $total = $total + 1
> else
> $total = 0
> end
>
>
> Sean O'Dell
>
>

Thanks! This was exactly what was needed and it works.

Just an additional note: from runtime performance it is much more
efficient to first initialize a variable and then use it. The code looks
cleaner then, too.

$total = 0
....

some loop
  $total += 1
end

Regards

    robert

···

> On Friday 02 July 2004 10:49, Randy Lawrence wrote: