sub new {
    my ($class) = @_;
    return bless {}, $class
}
[download]

That's because when you inherit from the class, the constructor will work for the new class, as well, without a need to write a new one specifying the subclass.

Thanks. the perldoc doesn't really say that clearly.

It's documented in perlobj to which bless links.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

Hi

Its has nothing to do with bless though, strict is protecting you from ambiguous code

$ splain < 2
perl -c packtest.pl
Bareword "PENDULUM" not allowed while "strict subs" in use at packates
+t.pl line
        9 (#1)
    (F) With "strict subs" in use, a bareword is only allowed as a
    subroutine identifier, in curly brackets or to the left of the "=>
+"
    symbol.  Perhaps you need to predeclare a subroutine?

packtest.pl had compilation errors (#2)
    (F) The final summary message when a perl -c fails.
[download]

ambiguous code (bareword PENDULUM)

$ perl -le" print bless {}, PENDULUM; "
PENDULUM=HASH(0x3f9adc)

$ perl -le" sub PENDULUM { 666 } print bless {}, PENDULUM;  "
666=HASH(0x3f9adc)
[download]

See Ill-Advised Uses of Barewords in modern_perl_2016_a4.pdf page 167

choroba helped with the immediate problem, but maybe an example of common usage will help:

use strict;
use warnings;

package Pendulum;

sub new {
    my ($class, %params) = @_;

    # Do interesting parameter validation here

    my $self = bless \%params, $class;

    # and other set up here. At this point you can call derived class 
+methods
    # as part of setup if you want using $self->methodName();

    return $self;
}


package main;

my $pit = Pendulum->new(Hz => 0.5);
[download]

Note in particular Pendulum->new(...) used to call the constructor

perlootut is a good start, in addition to the other docs mentioned herein. Actually I take that back, I may be misremembering how well done that was, but it doesn't even show a constructor using basic Perl.