more oop array

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Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: quoted-printable

In a module I have code that looks like this... sub add_widget=0A{=0A=
   =A0my $self =3D shift;  =A0 =A0my $new_widget =3D shift;  =
=A0 =A0push ( @{$self->{WIDGETS}}, $new_widget );=0A} sub get_widgets=
=0A{  =A0 =A0my $self =3D shift;  =A0 =A0return $self->{WIDGETS};=
=0A} I'm writing a test that is failing at runtime with the following =
error. Can't call method "attrib" on unblessed reference at ./test.pl =
line 40. $config =3D new Widget();=0Amy $i =3D 0;=0Afor ($i=3D0; $i<3;=
$i++)=0A{     my $w =3D new Widget();     $w->add_attrib("=
name", "widget".($i+1)); #add_attribute is tested and working     $=
config->add_widget($w); #this is what I'm testing=0A} foreach my $w ( =
$config->get_widgets() )=0A{  =A0 =A0#attrib is tested and working, but=
this foreach loop is not known to be valid code yet.     print $w=
->attrib("name"); # <----=A0 This is line 40.     print "\n";=0A}=
my expected output is... widget1=0Awidget2=0Awidget3 --=0AR=
onald Weidner
--0-1649666292-1315079697=:80328--

Re: more oop array

>>>>> "RW" == Ron Weidner writes:

first off, arrays have nothing (or little) to do with OOP. you are using
arrays inside an object but the code at that point is just plain perl.

RW> In a module I have code that looks like this...
RW> sub add_widget
RW> {
RW>    =A0my $self =3D shift;
RW>    =A0my $new_widget =3D shift;
RW>    =A0push ( @{$self->{WIDGETS}}, $new_widget );
RW> }

RW> sub get_widgets
RW> {
RW>    =A0my $self =3D shift;
RW>    =A0return $self->{WIDGETS};
RW> }

RW> I'm writing a test that is failing at runtime with the following erro=
r.

RW> Can't call method "attrib" on unblessed reference at ./test.pl line 4=
0.

RW> $config =3D new Widget();

you should call that with a direct method call and declare it with
my. also config is a bad name for a widget object, even in an example.

my $config =3D Widget->new();

RW> my $i =3D 0;
RW> for ($i=3D0; $i<3; $i++)

don't declare $i before the loop. it can be declared in it. also use
perl style loops and not c style when you can:

foreach my $i ( 0 .. 3 ) {


RW> {
RW>   =A0 my $w =3D new Widget();
RW>   =A0 $w->add_attrib("name", "widget".($i+1)); #add_attribute is =
tested and working

you don't show that method. also your comment's method name doesn't
agree with the actual method name. be consistant.


RW>   =A0 $config->add_widget($w); #this is what I'm testing

and where is the code for this?

RW> }

RW> foreach my $w ( $config->get_widgets() )
RW> {
RW>    =A0#attrib is tested and working, but this foreach loop is not=
known to be valid code yet.=20
RW>   =A0 print $w->attrib("name"); # <----=A0 This is line 40.=20

again, where is the code for this method? usually you can't debug method
calls without seeing the method code.

uri

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Re: more oop array

On 11-09-03 03:54 PM, Ron Weidner wrote:
> In a module I have code that looks like this...
>
> sub add_widget
> {
> my $self = shift;
> my $new_widget = shift;
> push ( @{$self->{WIDGETS}}, $new_widget );
> }
>
> sub get_widgets
> {
> my $self = shift;
> return $self->{WIDGETS};
> }
>
> I'm writing a test that is failing at runtime with the following error.
>
> Can't call method "attrib" on unblessed reference at ./test.pl line 40.
>
> $config = new Widget();
> my $i = 0;
> for ($i=0; $i<3; $i++)
> {
> my $w = new Widget();
> $w->add_attrib("name", "widget".($i+1)); #add_attribute is tested and working
> $config->add_widget($w); #this is what I'm testing
> }
>
> foreach my $w ( $config->get_widgets() )

foreach my $w ( @{ $config->get_widgets() } )
# get_widgets returns a ref to an array
# @{ $array_ref } deferences it


> {
> #attrib is tested and working, but this foreach loop is not known to be valid code yet.
> print $w->attrib("name"); #<---- This is line 40.
> print "\n";
> }
>
> my expected output is...
>
> widget1
> widget2
> widget3
>
> --
> Ronald Weidner


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Re: more oop array

On 03/09/2011 20:54, Ron Weidner wrote:
>
> In a module I have code that looks like this...
>
> sub add_widget
> {
> my $self = shift;
> my $new_widget = shift;
> push ( @{$self->{WIDGETS}}, $new_widget );
> }
>
> sub get_widgets
> {
> my $self = shift;
> return $self->{WIDGETS};
> }
>
> I'm writing a test that is failing at runtime with the following error.
>
> Can't call method "attrib" on unblessed reference at ./test.pl line 40.
>
> $config = new Widget();
> my $i = 0;
> for ($i=0; $i<3; $i++)
> {
> my $w = new Widget();
> $w->add_attrib("name", "widget".($i+1)); #add_attribute is tested and working
> $config->add_widget($w); #this is what I'm testing
> }

Hey Rod

You have been working to implement a module that presents an OO
interface, but you seem to have a poor grasp of Perl.

I have told you what I thought was wrong with your add_widget method,
but you seem to have implemented my fix without properly understanding
what was wrong.

We are not here to write and fix your code for you. It is time that you
put up your hands to say that the task is beyond you.

> foreach my $w ( $config->get_widgets() )
> {
> #attrib is tested and working, but this foreach loop is not known to be valid code yet.
> print $w->attrib("name"); #<---- This is line 40.
> print "\n";
> }

I suggest you think about what sort of value

$config->get_widgets

might be. Also, adding print statements to debug your code should help
a lot.

Cheers,

Rob

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Re: more oop array

On 03/09/2011 21:34, Uri Guttman wrote:
> Ron Weidner wrote:
>
> first off, arrays have nothing (or little) to do with OOP. you are using
> arrays inside an object but the code at that point is just plain perl.

That is a strange assertion. So OO software is more to do with scalars?
Or hashes? I will buy that Perl objects are generally blessed references
to hashes, but this is an anonymous array as the value of the base hash
object.

>> In a module I have code that looks like this...
>> sub add_widget
>> {
>> my $self = shift;
>> my $new_widget = shift;
>> push ( @{$self->{WIDGETS}}, $new_widget );
>> }

Ron, you would befriend more Perl authors here by dropping the
unnecessary parentheses:

push @{$self->{WIDGETS}}, $new_widget;

>> sub get_widgets
>> {
>> my $self = shift;
>> return $self->{WIDGETS};
>> }
>>
>> I'm writing a test that is failing at runtime with the following error.
>>
>> Can't call method "attrib" on unblessed reference at ./test.pl line 40.
>>
>> $config = new Widget();

That is an "indirect method call" and a nice syntax, especially because
it looks like C and reads like English, except that it is ambiguous.
Suffice to say that it is bad manners to call the constructor that way
(and even those who denounce it will have to look up why it is so bad).

> you should call that with a direct method call and declare it with
> my. also config is a bad name for a widget object, even in an example.

OK, so Uri says never to call an object $config, so $config2 should
suffice. It's not a Widget object Uri, it's the thing that has an array
of Widgets.

> my $config = Widget->new();

There is a big difference between

Widget->new();

and

Widget->new;

and more often than not you will want the latter. Much like

use MyModule;

is more likely to be right than

use MyModule ();

>> my $i = 0;
>> for ($i=0; $i<3; $i++)
>
> don't declare $i before the loop. it can be declared in it. also use
> perl style loops and not c style when you can:
>
> foreach my $i ( 0 .. 3 ) {

Yes about the declaration, but Uri means

foreach my $i (0 .. 2) {
:
}

>> {
>> my $w = new Widget();
>> $w->add_attrib("name", "widget".($i+1)); #add_attribute is tested and working
>
> you don't show that method. also your comment's method name doesn't
> agree with the actual method name. be consistant.

No he doesn't. But it's nothing to do with the problem Uri. Also, it's
'consistent'.

>> $config->add_widget($w); #this is what I'm testing
>
> and where is the code for this?

He hasn't shown it. Ron is a beginner.

>> }
>
>> foreach my $w ( $config->get_widgets() )
>> {
>> #attrib is tested and working, but this foreach loop is not known to be valid code yet.
>> print $w->attrib("name"); #<---- This is line 40.
>
> again, where is the code for this method? usually you can't debug method
> calls without seeing the method code.
>
> uri

So Uri skips over the likely cause of the problem: that the
'get_widgets' method probably returns an array reference rather than a
list.

My preference would be to write something similar to

my $widgets = $config->get_widgets;
foreach my $w (@$widgets) {
print $w->attrib("name");
print "\n";
}

Cheers,

Rob




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Re: more oop array

>>>>> "RD" == Rob Dixon writes:

RD> On 03/09/2011 21:34, Uri Guttman wrote:
>> Ron Weidner wrote:
>>
>> first off, arrays have nothing (or little) to do with OOP. you are using
>> arrays inside an object but the code at that point is just plain perl.

RD> That is a strange assertion. So OO software is more to do with scalars?
RD> Or hashes? I will buy that Perl objects are generally blessed references
RD> to hashes, but this is an anonymous array as the value of the base hash
RD> object.

actually in this example a hash ref is the object. the array in question
is a ref inside the hash. so if you ripped out all the OO code, it would
still have the same issues as he has now. or put it another way, he has
both OO and array issues in his code. but he has no array OO issue. :)

>>>
>>> Can't call method "attrib" on unblessed reference at ./test.pl line 40.
>>>
>>> $config = new Widget();

RD> That is an "indirect method call" and a nice syntax, especially because
RD> it looks like C and reads like English, except that it is ambiguous.
RD> Suffice to say that it is bad manners to call the constructor that way
RD> (and even those who denounce it will have to look up why it is so bad).

>> you should call that with a direct method call and declare it with
>> my. also config is a bad name for a widget object, even in an example.

RD> OK, so Uri says never to call an object $config, so $config2 should
RD> suffice. It's not a Widget object Uri, it's the thing that has an array
RD> of Widgets.

so @widgets or whatever. but it isn't a config in any way shape or
form. name should reflect the usage of the data, not be just a
placeholder or mnemonic.

>> my $config = Widget->new();

RD> There is a big difference between

Widget-> new();

RD> and

Widget-> new;

RD> and more often than not you will want the latter. Much like

not for method calls. both pass no args other than the object itself.

RD> use MyModule;

RD> is more likely to be right than

RD> use MyModule ();

that is a very different case as perl itself is parsing and handling
that and will call the import method differently based on it.

>>> my $i = 0;
>>> for ($i=0; $i<3; $i++)
>>
>> don't declare $i before the loop. it can be declared in it. also use
>> perl style loops and not c style when you can:
>>
>> foreach my $i ( 0 .. 3 ) {

RD> Yes about the declaration, but Uri means

RD> foreach my $i (0 .. 2) {

off by one error. common enough. it is why c style loops are harder to
read. my error make a good case for this.

>> you don't show that method. also your comment's method name doesn't
>> agree with the actual method name. be consistant.

RD> No he doesn't. But it's nothing to do with the problem Uri. Also, it's
RD> 'consistent'.

no it isn't consistant. the name in the comment wasn't the same name in
the call. how you call that consistant is the question.

>>> $config->add_widget($w); #this is what I'm testing
>>
>> and where is the code for this?

RD> He hasn't shown it. Ron is a beginner.

right. i am asking him to show all the related code as a teaching
point.

>>> }
>>
>>> foreach my $w ( $config->get_widgets() )
>>> {
>>> #attrib is tested and working, but this foreach loop is not known to be valid code yet.
>>> print $w->attrib("name"); #<---- This is line 40.
>>
>> again, where is the code for this method? usually you can't debug method
>> calls without seeing the method code.
>>
>> uri

RD> So Uri skips over the likely cause of the problem: that the
RD> 'get_widgets' method probably returns an array reference rather than a
RD> list.

i didn't look into that. you seem to be in a poor mood again. please be
more careful when you are in such a mood.

uri

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Re: more oop array

On 03/09/2011 22:25, Uri Guttman wrote:
>>>>>> "RD" == Rob Dixon writes:
>
> RD> On 03/09/2011 21:34, Uri Guttman wrote:
> >> Ron Weidner wrote:
> >>
> >> first off, arrays have nothing (or little) to do with OOP. you are using
> >> arrays inside an object but the code at that point is just plain perl.
>
> RD> That is a strange assertion. So OO software is more to do with scalars?
> RD> Or hashes? I will buy that Perl objects are generally blessed references
> RD> to hashes, but this is an anonymous array as the value of the base hash
> RD> object.
>
> actually in this example a hash ref is the object. the array in question
> is a ref inside the hash. so if you ripped out all the OO code, it would
> still have the same issues as he has now. or put it another way, he has
> both OO and array issues in his code. but he has no array OO issue. :)

Maybe I misunderstood. Were you saying that the subject line of Ron's
post shouldn't have mentioned OOP? That would suppose that he knew the
answer to his question before posting it. Or were you perhaps trying to
simplify the concept by saying that object-orientation is irrelevant?

> >>>
> >>> Can't call method "attrib" on unblessed reference at ./test.pl line 40.
> >>>
> >>> $config = new Widget();
>
> RD> That is an "indirect method call" and a nice syntax, especially because
> RD> it looks like C and reads like English, except that it is ambiguous.
> RD> Suffice to say that it is bad manners to call the constructor that way
> RD> (and even those who denounce it will have to look up why it is so bad).
>
> >> you should call that with a direct method call and declare it with
> >> my. also config is a bad name for a widget object, even in an example.
>
> RD> OK, so Uri says never to call an object $config, so $config2 should
> RD> suffice. It's not a Widget object Uri, it's the thing that has an array
> RD> of Widgets.
>
> so @widgets or whatever. but it isn't a config in any way shape or
> form. name should reflect the usage of the data, not be just a
> placeholder or mnemonic.

Again I am lost. It isn't a 'widget object' it is an object that,
probably amongst other things, contains an array of widgets. Perhaps you
are saying that any such object (perhaps a GUI-related one) couldn't
possibly be a configuration in any sense? I find that a long stretch.

> >> my $config = Widget->new();
>
> RD> There is a big difference between
>
> RD> Widget->new();
>
> RD> and
>
> RD> Widget->new;
>
> RD> and more often than not you will want the latter. Much like
>
> not for method calls. both pass no args other than the object itself.

I agree, except that the first parameter here is the class (package)
name rather than an object.

> RD> use MyModule;
>
> RD> is more likely to be right than
>
> RD> use MyModule ();
>
> that is a very different case as perl itself is parsing and handling
> that and will call the import method differently based on it.

Yes. I withdraw this point.

> >>> my $i = 0;
> >>> for ($i=0; $i<3; $i++)
> >>
> >> don't declare $i before the loop. it can be declared in it. also use
> >> perl style loops and not c style when you can:
> >>
> >> foreach my $i ( 0 .. 3 ) {
>
> RD> Yes about the declaration, but Uri means
>
> RD> foreach my $i (0 .. 2) {
>
> off by one error. common enough. it is why c style loops are harder to
> read. my error make a good case for this.

We agree completely here. I was correcting something that I assumed was
an oversight on your part.

> >> you don't show that method. also your comment's method name doesn't
> >> agree with the actual method name. be consistant.
>
> RD> No he doesn't. But it's nothing to do with the problem Uri. Also, it's
> RD> 'consistent'.
>
> no it isn't consistant. the name in the comment wasn't the same name in
> the call. how you call that consistant is the question.

I was being picky and correcting your spelling. Just as you were being
picky and correcting his comments!

> >>> $config->add_widget($w); #this is what I'm testing
> >>
> >> and where is the code for this?
>
> RD> He hasn't shown it. Ron is a beginner.
>
> right. i am asking him to show all the related code as a teaching
> point.

I don't think your comment conveys a polite request to see the rest of
the code, I think it sounds like a telling off directed at someone who
should know better. But as a beginner I am sure he thought he had posted
what was relevant.

> >>> }
> >>
> >>> foreach my $w ( $config->get_widgets() )
> >>> {
> >>> #attrib is tested and working, but this foreach loop is not known to be valid code yet.
> >>> print $w->attrib("name"); #<---- This is line 40.
> >>
> >> again, where is the code for this method? usually you can't debug method
> >> calls without seeing the method code.
> >>
> >> uri
>
> RD> So Uri skips over the likely cause of the problem: that the
> RD> 'get_widgets' method probably returns an array reference rather than a
> RD> list.
>
> i didn't look into that. you seem to be in a poor mood again. please be
> more careful when you are in such a mood.

Not at all. I was once highly distressed and needed to apologise for a
post I made, and I hope I won't now be forever damned as being in a foul
mood whenever I disagree with you. My wife is an excellent indicator of
whether or not I am in a bad mood, and she would very quickly have said
something if I was overly irritable that night.

Ron shows this code

sub add_widget {
my $self = shift;
my $new_widget = shift;
push ( @{$self->{WIDGETS}}, $new_widget );
}

sub get_widgets {
my $self = shift;
return $self->{WIDGETS};
}

So get_widgets can only ever return a scalar, and presumably it is
meant to be an array reference.

foreach my $w ( $config->get_widgets() ) {
print $w->attrib("name"); # <---- This is line 40.
}

That looks very much like $config->get_widgets needs to be dereferenced
to an array. As it is, the print statement is trying to call

$config->{WIDGETS}->attrib("name");

and because $config->{WIDGETS} is an unblessed reference, the error
message is delivered

Can't call method "attrib" on unblessed reference

None of this reasoning needs sight of more of the code, better comments,
or different variable names, and while those points may be useful as
gentle suggestions you seem to have completely failed to answer Ron's
question.

Rob

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