Re: Caching a default instance to avoid initializing it every time (with Moo)

It kinda looks like a singleton, except not exactly so I don't know if Moo can do this. But maybe since what you want is neither of the two behaviours you might expect for a class (always a new instance, or always the same), this can be done in a separate function, rather than the constructor?

my $default;
sub get_instance {
  my ($class, %args) = @_;

  return $default ||= $class->new unless %args;
  return $class->new(%args);
}
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Re^2: Caching a default instance to avoid initializing it every time (with Moo) by karlgoethebier (Abbot) on Feb 09, 2018 at 10:45 UTC
"...looks like a singleton...I don't know if Moo can do this..." Probably this can be easily done with Role::Singleton by just saying `with 'Role::Singleton';`? I never used this and stumbled over it by chance. Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť `perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'`Help	[reply] [d/l] [select]
Re^3: Caching a default instance to avoid initializing it every time (with Moo) by Eily (Monsignor) on Feb 09, 2018 at 10:52 UTC
You'd still have to write a wrapper if you want a single interface to sometimes provide a new instance, sometimes the singleton. But I like that this interface leaves the choice to the caller, you can either have a new instance, regardless of input, or the singleton when you know it can work.	[reply]
Re^3: Caching a default instance to avoid initializing it every time (with Moo) by Dallaylaen (Chaplain) on Jul 01, 2018 at 11:22 UTC
Ended up going that way in the end. Thanks!	[reply]
Re^4: Caching a default instance to avoid initializing it every time (with Moo) by karlgoethebier (Abbot) on Jul 01, 2018 at 11:50 UTC
Nice to hear. Good things need a while (My best Denglish ever) 😎. Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť `perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'`Help	[reply] [d/l]
Re^2: Caching a default instance to avoid initializing it every time (with Moo) by Dallaylaen (Chaplain) on Feb 16, 2018 at 10:53 UTC
I ended up going that way because `around new` wasn't welcome by the team. However, from my point of view caching a read-only object should be transparent to the user of the class as long as it's documented and there's a way to really instantiate a new object if one wants to.	[reply]