Warning: instance variable @foo not initialized

Ruby
1

Running some simple tests with Prawn, I am getting thousands of lines
of warnings from Ruby 1.9.1:

/usr/local/lib/ruby/gems/1.9.1/gems/prawn-layout-0.3.2/lib/prawn/table/cell.rb:255:
warning: instance variable @text_color not initialized

There are hundreds of these, and they seem to come from a lot of usages
like:

e.text_color ||= @text_color

or this kind of usage:

  def page_content
    @active_stamp_stream || @store[@page_content]
  end

In the latter case, @store is apparently fine, it’s just
@active_stamp_screen
which is uninitialized.

Should I infer that the library should be setting these all to nil in
its
initialize()?

-s

2

On Tuesday 24 November 2009, Seebs wrote:

|
|initialize()?
|
|-s
|

When an instance variable is referred to before a value has been
assigned to
it, it automatically gets the value nil and the warning you see is
emitted.
The reason for the warning, I guess, is to help finding situations where
you
make a mistake writing the name of the variable. For example, in the
following
code

@var = 4
if @vra < 5
…

@vra in the second line should obviously have been @var. Without the
varning,
it would have been easy to overlook this mistake (expecially if the
variable
name was longer than only three characters). The warning helps spotting
it.

To answer your question: the library should have set those variable to
nil
before using them, if it wanted to avoid the warning (not necessarily in
initialize, just before the variables were used). Not doing so, however,
is
perfectly correct, if you don’t mind seeing the warnings. Personally, I
don’t
like them, so I always assign instance variables before using them.

I hope this helps

Stefano

3

On Tuesday 24 November 2009, Seebs wrote:

|> I hope this helps
|
|It does. I guess I’m a bit confused, 'cuz on the one hand, Prawn looks
|pretty nice, but on the other hand, getting thousands of lines of warnings
|running a simple test program sorta worries me.
|
|-s
|

As I said, there’s nothing wrong with not initializing instance
variables to
nil: it’s a matter of preferences. It seems Prawn’s author doesn’t like
to
initialize variables to nil (indeed, it looks a bit too C-like for ruby)
and
doesn’t mind some warnings.

If the warnings only annoy you, you should be able to disable them by
not
passing the -w option to ruby. If instead you’re worried that they can
mean
there’s something wrong, I think you don’t need to. Most of the times,
warnings issued by ruby are harmless.

Stefano

4

On 2009-11-24, Stefano C. [email protected] wrote:

To answer your question: the library should have set those variable to nil
before using them, if it wanted to avoid the warning (not necessarily in
initialize, just before the variables were used). Not doing so, however, is
perfectly correct, if you don’t mind seeing the warnings. Personally, I don’t
like them, so I always assign instance variables before using them.

Thanks!

I hope this helps

It does. I guess I’m a bit confused, 'cuz on the one hand, Prawn looks
pretty nice, but on the other hand, getting thousands of lines of
warnings
running a simple test program sorta worries me.

-s

5

On 2009-11-24, Stefano C. [email protected] wrote:

If the warnings only annoy you, you should be able to disable them by not
passing the -w option to ruby. If instead you’re worried that they can mean
there’s something wrong, I think you don’t need to. Most of the times,
warnings issued by ruby are harmless.

There’s two issues.

  1. Actually, those warnings happen even without -w. (Unless there’s
    something non-obvious passing the -w to Ruby that I didn’t think about.)
  2. I actually really DO want -w warnings for my code. Is there a way
    to
    do a require that suppresses warnings during parsing of the required
    code?

-s

6

Seebs wrote:

Is there a way
to
do a require that suppresses warnings during parsing of the required
code?

Yes - but note that these are run-time, not parse-time warnings.

def quietly
ov = $VERBOSE
$VERBOSE = nil
yield
ensure
$VERBOSE = ov
end

quietly { p @foo }

7

On Tuesday 24 November 2009, Seebs wrote:

|2. I actually really DO want -w warnings for my code. Is there a way to
|do a require that suppresses warnings during parsing of the required code?
|
|-s
|

I never used Prawn, so I can’t tell why it issues warnings even without
the -w
option. However, you can control this setting from inside your code
using the
$VERBOSE global variable. It is initially set by ruby to one of the
following
values:

  • true if the -w, -v or --verbose flags have been passed on the command
    line
  • nil if the -W0 flag has been passed on the command line
  • false if none of the above flags has been given

You can change it from inside your code to avoid warnings from Prawn:

#your code
…
old_verbose = $VERBOSE
$VERBOSE = nil
#code which makes prawn issue warnings
…
$VERBOSE = old_verbose

Stefano

8

2009/11/24 Seebs [email protected]:

On 2009-11-24, Stefano C. [email protected] wrote:

If the warnings only annoy you, you should be able to disable them by not
passing the -w option to ruby. If instead you’re worried that they can mean
there’s something wrong, I think you don’t need to. Most of the times,
warnings issued by ruby are harmless.

There’s two issues.

  1. Actually, those warnings happen even without -w. (Unless there’s
    something non-obvious passing the -w to Ruby that I didn’t think about.)

This is not what I am seeing:

$ allruby -e ‘p @foo’
CYGWIN_NT-5.1 padrklemme1 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin

ruby 1.8.7 (2008-08-11 patchlevel 72) [i386-cygwin]
nil

ruby 1.9.1p129 (2009-05-12 revision 23412) [i386-cygwin]
nil
$ allruby -we ‘p @foo’
CYGWIN_NT-5.1 padrklemme1 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin

ruby 1.8.7 (2008-08-11 patchlevel 72) [i386-cygwin]
-e:1: warning: instance variable @foo not initialized
nil

ruby 1.9.1p129 (2009-05-12 revision 23412) [i386-cygwin]
-e:1: warning: instance variable @foo not initialized
nil
$

  1. I actually really DO want -w warnings for my code. Is there a way to
    do a require that suppresses warnings during parsing of the required code?

You can use -W to have a bit more control over verbosity.

Kind regards

robert

9

On 2009-11-24, Robert K. [email protected] wrote:

This is not what I am seeing:

I’m assuming I must have something I’m not thinking of (a makefile or
something) passing a -w that I’m not aware of.

-s

10

On 2009-11-24, Brian C. [email protected] wrote:

Yes - but note that these are run-time, not parse-time warnings.

D’oh. Spot the forgetful C programmer.

So what I really want is a way to request that a particular chunk of
code
have interpreter warnings disabled while running it, or to find out
whether
the Prawn people would accept a patch to eliminate these.

-s

11

On 11/25/2009 05:08 AM, Seebs wrote:

On 2009-11-24, Robert K. [email protected] wrote:

This is not what I am seeing:

I’m assuming I must have something I’m not thinking of (a makefile or
something) passing a -w that I’m not aware of.

Or you used option -v:

-v print version number, then turn on verbose mode

Kind regards

robert

12

Seebs wrote:

On 2009-11-24, Brian C. [email protected] wrote:

Yes - but note that these are run-time, not parse-time warnings.

D’oh. Spot the forgetful C programmer.

So what I really want is a way to request that a particular chunk of
code
have interpreter warnings disabled while running it

That’s what I already posted:

quietly do
… any code you like, e.g. build a document using prawn
end

13

On 2009-11-25, Robert K. [email protected] wrote:

I’m assuming I must have something I’m not thinking of (a makefile or
something) passing a -w that I’m not aware of.

Or you used option -v:

Nope! It turns out that I was using
ruby foo.rb
but “foo.rb” started with “#!/usr/local/bin/ruby -w”, and apparently the
interpreter parses that even when ruby is invoked explicitly.

-s