How do I inherit subroutines in Perl with 'use base'?
Solution 1
The C++ mechnics aren't much different than the Perl mechanics: To use inheritance, you need two classes: the base class and the inheriting class. But you don't have any descendent class.
You are also lacking a constructor. Unlike C++, Perl will not provide a default constructor for you.
Your base class contains a bad syntax error, so I guess you didn't try the code before posting.
Finally, as tsee already observed, you will have to let Perl know whether you want a function call or a method call.
What you really want would look something like this:
my $foo = TestDescendent->new();
$foo->main();
package TestBase;
sub new {
my $class = shift;
return bless {}, $class;
}
sub tbSub
{
my ($self, $parm) = @_;
print "\nTestBase: $parm\n";
}
package TestDescendent;
use base 'TestBase';
sub main {
my $self = shift;
$self->mySub( 1 );
$self->tbSub( 2 );
$self->mySub( 3 );
}
sub mySub
{
my $self = shift;
my $parm = shift;
print "\nTester: $parm\n";
}
1;
Solution 2
You should have a look at using Moose which is a postmodern object system for Perl5. You will probably find it a lot easier to grasp than using standard Perl OO semantics... especially when coming from another OO language.
Here's a Moose version of your question....
package TestBase;
use Moose;
sub tbSub {
my ($self, $parm) = @_;
print "\nTestBase: $parm\n";
}
package TestDescendent;
use Moose;
extends 'TestBase';
sub main {
my $self = shift;
$self->mySub( 1 );
$self->tbSub( 2 );
$self->mySub( 3 );
}
sub mySub {
my ($self, $parm) = @_;
print "\nTester: $parm\n";
}
package main;
my $foo = TestDescendent->new();
$foo->main
The differences are....
- Constructor automatically created for you &
- Inheritance defined by "extends" command instead of "use base".
So this example only covers the tip of the Moose iceberg ;-)
Solution 3
As a sidenote, there is little good reason to use base
rather than the newer use parent
.
Solution 4
It seems to me, you are mixing up two things here: Object-Oriented and Procedural Perl. Perl OO is kind of "different" (as in not mainstream but workable).
Your TestBase.pm module seems to expect to be run as a Perl object (Perl oo-style), but your Perl script wants to access it as "normal" module. Perl doesn't work the way C++ does (as you realised) so you would have to construct your code differently. See Damian Conway's books for explanations (and smarter code than mine below).
Procedural:
#! /usr/bin/perl
#The module to inherit from
package TestBase;
use strict;
use warnings;
use Exporter ();
our @ISA = qw (Exporter);
our @EXPORT = qw (tbSub);
#-------------------------------
sub tbSub
{
my ($parm) = @_;
print "\nTestBase: $parm\n";
}
1;
.
#! /usr/bin/perl
#The descendent class
use strict;
use warnings;
use TestBase;
sub main;
sub mySub;
#-------------------------------
#Entry point...
main();
#---code------------------------
sub main
{
mySub(1);
tbSub(2);
mySub(3);
}
#-------------------------------
sub mySub
{
my $parm = shift;
print "\nTester: $parm\n";
}
Perl OO
#! /usr/bin/perl
#The base class to inherit from
package TestBase;
use strict;
use warnings;
#-------------------------------
sub new { my $s={ };
return bless $s;
}
sub tbSub
{
my ($self,$parm) = @_;
print "\nTestBase: $parm\n";
}
1;
.
#! /usr/bin/perl
#The descendent class
use strict;
use warnings;
use TestBase;
sub main;
sub mySub;
#-------------------------------
#Entry point...
main();
#---code------------------------
sub main
{
my $tb = TestBase->new();
mySub(1);
$tb->tbSub(2);
mySub(3);
}
#-------------------------------
sub mySub
{
my $parm = shift;
print "\nTester: $parm\n";
}
Solution 5
Perl's inheritance inherits methods, not functions. That means you will have to call
main->tbSub(2);
However, what you really want is to inherit the method into a proper class:
package Derived;
use base "TestBase";
package main;
Derived->somemethod("foo");
Calling methods in the current package as functions won't pass in the $self or "this" object nor the class name magically. Internally,
Class->somemethod("foo")
essentially ends up being called as
Class::somemethod("Class", "foo")
internally. Of course, this assumes Class has a subroutine/method named "somemethod". If not, the superclasses of Class will be checked and if those don't have a method "somemethod" either, you'll get a fatal error. (Same logic applies for $obj->method("foo").)
slashmais
Updated on June 15, 2022Comments
-
slashmais about 2 years
How do I apply 'use base' in Perl to inherit subs from some base module?
I'm used to C++ inheritance mechanics, and all the sites I googled for this caused more confusion then help. I want to do something like the following:
#! /usr/bin/perl #The base class to inherit from use strict; use warnings; package 'TestBase'; #------------------------------- sub tbSub { my ($self, $parm) = @_; print "\nTestBase: $parm\n"; } 1;
.
#! /usr/bin/perl #The descendent class use strict; use warnings; use base qw(TestBase); sub main; sub mySub; #------------------------------- #Entry point... main(); #---code------------------------ sub main { mySub(1); tbSub(2); mySub(3); } #------------------------------- sub mySub { my $parm = shift; print "\nTester: $parm\n"; }
Perl complains/cannot find tbSub.