Re^4: Qualified package variable access ( private methods )

> we certainly should not call them "private" because that has an established, widely understood meaning which is different from what these variables are. I refer to private members of classes in OO languages such as C++ and Java.

I'm neither an expert on C++ nor Java.

Could you please explain the semantic difference to this demo of private methods achieved with my ?

use strict;
use warnings;
use 5.10.0;


# ========================================
#          class definition
# ========================================

{
    package Class;

    use Carp qw/cluck/;
    use Data::Dump qw/pp dd/;

    # ----- constructor

    sub new {
        my ($class,@init)=@_;

        return bless {@init}, $class;
    }

    # ----- private methods

    my $private = sub {
        my ($self) = @_;

        cluck "I'm a PRIVATE METHOD of OBJ= " . pp $self ;
    };


    # ----- public methods
    sub public {
        my ($self) = @_;

        cluck "I'm a PUBLIC METHOD of OBJ= " . pp $self ;
        warn " ... calling private methods...\n";

        $self->$private();
    }

}



# ========================================
#                 demo
# ========================================

package main;

my $obj = Class->new( ID => 1 );
my $obj2 = Class->new( ID => 2 );

$obj->public;
$obj2->public;



$obj->private;       # fails
#$obj->$private;     # doesn't compile
[download]

-*- mode: compilation; default-directory: "d:/tmp/pm/" -*- Compilation started at Sat Dec 19 16:53:21 C:/Perl_524/bin\perl.exe -w d:/tmp/pm/private_method.pl I'm a PUBLIC METHOD of OBJ= bless({ ID => 1 }, "Class") at d:/tmp/pm/p +rivate_method.pl line 37. Class::public(Class=HASH(0x1cc1e0)) called at d:/tmp/pm/private_me +thod.pl line 56 ... calling private methods... I'm a PRIVATE METHOD of OBJ= bless({ ID => 1 }, "Class") at d:/tmp/pm/ +private_method.pl line 29. Class::__ANON__(Class=HASH(0x1cc1e0)) called at d:/tmp/pm/private_ +method.pl line 40 Class::public(Class=HASH(0x1cc1e0)) called at d:/tmp/pm/private_me +thod.pl line 56 I'm a PUBLIC METHOD of OBJ= bless({ ID => 2 }, "Class") at d:/tmp/pm/p +rivate_method.pl line 37. Class::public(Class=HASH(0x1cc0d8)) called at d:/tmp/pm/private_me +thod.pl line 57 ... calling private methods... I'm a PRIVATE METHOD of OBJ= bless({ ID => 2 }, "Class") at d:/tmp/pm/ +private_method.pl line 29. Class::__ANON__(Class=HASH(0x1cc0d8)) called at d:/tmp/pm/private_ +method.pl line 40 Class::public(Class=HASH(0x1cc0d8)) called at d:/tmp/pm/private_me +thod.pl line 57 Can't locate object method "private" via package "Class" at d:/tmp/pm/ +private_method.pl line 61. Compilation exited abnormally with code 255 at Sat Dec 19 16:53:22
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery}

Comment on Re^4: Qualified package variable access ( private methods ) Select or Download Code

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Re^5: Qualified package variable access ( private methods ) by jdporter (Paladin) on Dec 21, 2020 at 19:00 UTC
Well, one major difference is that that `$private` is not a member of the class at all, it is a lexical in the same block in which you've defined the subs of the class. And, of course, it's singleton. A class private in C++/Java is not singleton. It could be declared 'static', which would make it singleton; but that still wouldn't be the same as what you've shown. If your `$private` were truly equivalent, you'd be able to write this: `use strict; use warnings; { package Class; my $n = 42; sub new { my $pkg = shift; bless {}, $pkg; } sub foo; } sub Class::foo { print "$n\n"; }` [download] But you can't, of course, because $n is out of scope at that point. It is not a member of the "class". I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.	[reply] [d/l] [select]
Re^6: Qualified package variable access ( private methods ) by LanX (Saint) on Dec 21, 2020 at 20:36 UTC
> But you can't, of course, because $n is out of scope at that point. It is not a member of the "class". I was aware of the scoping/closure effect, but I very rarely see Perl code where class definitions are dispersed over more the one file. I.O.W file scope is sufficient. And I think we aggree that Perl allows so many kinds of introspection (e.g. PadWalker) that privacy becomes relative. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]


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