http://www.perlmonks.org?node_id=996036


in reply to Re: Math::BigInt new
in thread Math::BigInt new

Agreed. However, here is the first part of new: 
sub new 
  {
  # create a new BigInt object from a string or another BigInt object.
+ 
  # see hash keys documented at top

  # the argument could be an object, so avoid ||, && etc on it, this w
+ould
  # cause costly overloaded code to be called. The only allowed ops ar
+e
  # ref() and defined.

  my ($class,$wanted,$a,$p,$r) = @_;
 
  # avoid numify-calls by not using || on $wanted!
  return $class->bzero($a,$p) if !defined $wanted;    # default to 0
  return $class->copy($wanted,$a,$p,$r)
   if ref($wanted) && $wanted->isa($class);        # MBI or subclass

  $class->import() if $IMPORT == 0;        # make require work
  
  my $self = bless {}, $class;

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If it gets to the last line, and $class == 27, then $class must have been changed somewhere?

And generally speaking, if I want a new object from an existing object, shouldn't the existing object be able to create one for me? Or do I have to go around doing this? 

my $y = {ref $x}->new();

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(or whatever the syntax is for that)

-QM
--
Quantum Mechanics: The dreams stuff is made of

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Re^3: Math::BigInt new
by tobyink (Canon) on Sep 27, 2012 at 16:13 UTC

    $class is the same as $x (i.e. the bigint 27) the whole way through new, and bless implicitly stringifies its second argument (like print implicitly stringifies its arguments).

    ref($x)->new(48) should do what you want. Another reasonably common idiom is:

    my $new = (ref($existing) // $existing)->new(...)

    [download]

    This allows $existing to be either an existing object or a class name.

    perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'
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[d/l]
[select]
Re^3: Math::BigInt new
by remiah (Hermit) on Sep 27, 2012 at 23:12 UTC

    I also think this is strange. There is no checking for ref($class). I guess something like ... 

        if ( ref($class) ){
        my $t = $wanted; 
        $t =~ s/^[+-]//;

        return bless {
            sign => $class->{sign},
            value => $CALC->_new($t),
        }, ref($class);
    }

    [download]
    should be in new constructor, doesn't it?

[reply]
[d/l]

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