Autoboxing by subclassing CORE

This is a slightly silly thing that I've recently been surprised to discover actually works...

{
    package String;
    use base 'CORE';
    use overload
        q[bool]   => '_deref',
        q[""]     => '_deref',
        q[0+]     => '_deref',
        fallback  => 1,
    ;
    sub new {
        my ($class, $str) = @_;
        bless \$str => $class;
    }
    sub _deref {
        ${$_[0]};
    }
}

my $greeting = String->new("Hello World\n");
print $greeting->substr(6);
[download]

It's not really obfuscated, but even experienced Perl programmers would probably do a double-take when seeing it, and I couldn't think of a better section to put it in.

By the way, you can also use CORE directly - the subclassing is not strictly necessary.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

Comment on Autoboxing by subclassing CORE Download Code

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Re: Autoboxing by subclassing CORE by moritz (Cardinal) on Jun 20, 2012 at 15:11 UTC
Nice :-). FWIW this is autounboxing you are demonstrating; autoboxing would be `"Hello World\n"->substr(6)` working. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re: Autoboxing by subclassing CORE by choroba (Cardinal) on Jun 20, 2012 at 21:19 UTC
What version of Perl is needed to make it run? I am getting `Can't locate object method "substr" via package "String" at - line 20.` [download] in 5.14.2.	[reply] [d/l]
Re^2: Autoboxing by subclassing CORE by tobyink (Canon) on Jun 21, 2012 at 00:57 UTC
I'm using 5.16. perl5160delta notes various improvements to the CORE and CORE::GLOBAL namespaces. Perhaps in earlier Perls `CORE::substr` doesn't work, but some other interesting CORE functions are likely to work. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l]
Re: Autoboxing by subclassing CORE by ambrus (Abbot) on Oct 09, 2012 at 21:05 UTC
Wow, this might be the first obfu posted here that requires perl 5.16 in an essential way. Nice.	[reply]
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