Re^5: Calling module function from within a blessed module

Naming a package 0 is a fatal, compilation error ... The problem is likely to occur where, in some code completely separate from yours, someone writes '$x->your_method()' when, perhaps, '$y->your_method()' was intended.

Another example might be auto-generated package names (though if such code generated a package named "0", one could question the sanity of that choice...)

use warnings;
use strict;

{ package Foo;
    use Data::Dump;
    use Scalar::Util qw/blessed/;
    sub new { return bless {}, shift }
    sub foo {
        my $self = shift if blessed($_[0]) && $_[0]->isa(__PACKAGE__);
        dd 'foo', $self, \@_;
    }
    sub bar {
        my $self = shift if defined blessed($_[0])
            && $_[0]->isa(__PACKAGE__);
        dd 'bar', $self, \@_;
    }
}

{ no strict 'refs'; @{"0::ISA"} = ('Foo') }

my $x = bless {}, '0';
$x->foo();  # ("foo", undef, ["0=HASH(0x561239194f3e)"])
$x->bar();  # ("bar", "0=HASH(0x561239194f3e)", [])
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Re^6: Calling module function from within a blessed module by kcott (Archbishop) on Jan 02, 2021 at 21:31 UTC
The general idea I trying to get across — and, perhaps, didn't explain sufficiently well — was that problems are less likely to occur from a hard-coded package name, but rather from accidentally using an incorrect variable; the likelihood of which is exacerbated by poorly chosen (especially single-letter) variable names. The type of scenario I envisaged, involved `$x` being used for some purpose, and ultimately ending up with a value of zero. Later in the code, a variable to represent either an `X` class, or an object thereof, was wanted. As `$x` was already taken, the coder chose the next available, single-letter variable, `$y`. Subsequently, and paraphasing your example, the intuitive but incorrect `@{"${x}::ISA"}` and `bless {}, $x` was used; when, of course, the unintuitive yet correct `@{"${y}::ISA"}` and `bless {}, $y` was needed. Possibly getting a little off-topic (and hopefully not heading towards too much of a rant) but, in the main, meaningful names should be used, and single-letter names should be generally avoided. There are a few well-known examples where single-letter names are fine; e.g. `sort { $a <=> $b }` and in the limited scope of `for my $i (0..$#ary)`. I also use them in one-liners and short example code. Other than that, I always aim to use meaningful names. — Ken	[reply] [d/l] [select]
Re^7: Calling module function from within a blessed module by haukex (Archbishop) on Jan 03, 2021 at 10:34 UTC
The general idea I trying to get across — and, perhaps, didn't explain sufficiently well — was that problems are less likely to occur from a hard-coded package name, but rather from accidentally using an incorrect variable; the likelihood of which is exacerbated by poorly chosen (especially single-letter) variable names. Sorry, I probably should have said: I think your example is good, I was just giving another scenario `:-)`	[reply] [d/l]
Re^8: Calling module function from within a blessed module by kcott (Archbishop) on Jan 03, 2021 at 21:18 UTC
No need to apologise; your example was also good. Any fault probably lies with me; as stated: "I ... perhaps, didn't explain sufficiently well". — Ken	[reply]