perl - Invocation of SUPER::new() -

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i've seen 2 ways implement new method in derived class.

method one:

sub new {     $invocant = shift;     $class   = ref($invocant) || $invocant;      $self = {};     bless($self, $class);     $self = $self->super::new( @_ );     return($self); }

method two:

sub new {   $self = shift;   $class = ref($self) || $self;   return $self if ref $self;   $base_object = $class->super::new(@_);   return bless ($base_object, $class); }

i'm not sure understand difference is. can please explain?

from comments , answers can see ref() part bad.

but use of super::new(@_)? in first example, hashref blessed derived class , object's super's new called , saved same object.

in second example on other hand, base object created class's supers new method , blessed new class.

what difference between these 2 ways? looks first overwrites object base object. second seems "double-bless". i'm confused.

update

you ask:

what difference between these 2 ways? looks first overwrites object base object. second seems "double-bless". i'm confused.

take heart. each of 2 methods show confused, , neither should emulated.

method 1 blesses object of class derivedclass existence , uses object call allocator/constructor of ancestorclass, replacing itself. now, ancestorclass::new uses unfortunate ref($yuck) || $yuck idiom, means new object blessed derivedclass. so, 1 derivedclass object used construct replace it. dubious.

method 2 returns receiver ($self) if receiver object. (note ref($self) checked twice when need checked once.) is, $o->new() returns same $o under method two. if receiver not object class name, is, if instead had called derivedclass->new, ancestorclass::new called. first argument superclass' method 'derivedclass', , presumably superclass not hardcode blessed package name, subsequent re-blessing pointless.

just don't worry these examples. instead please consult perlobj , perlootut safe , sane uses of super.

original answer

augh, eyes!

method 1 is, daxim commented, objectionable means of allowing 1 construct object same class existing object:

my $o1 = methodone->new(); $o2 = $o1->new();        # $o2 clone of $o1.  no, wait, isn't!                             # it's brand new, "empty" object.  ha,                             # fooled you.

method 2 (i think) a workaround confusing practice. method 2 return very same object if new() called.

my $o1 = methodtwo->new(); $o2 = $o1->new();         # $o2 new methodtwo.  no, wait, isn't!                              # it's brand new object.  no, wait, isn't!                              # it's /exactly same object/ $o1.  ha,                              # fooled you.

don't use either. :) there may applications either of above semantics make perfect sense. wouldn't name method new() in applications...


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