basic object-oriented Perl question

[DoraC]

hi

I can't seem to figure out how to properly implement inheritance. I have one base class that I would like a variety of other classes to inherit from - but every time I try to code this (following my books or internet examples) I run into problems. I have the base class defined in one module (base.pm), and the children-to-be in others (say, child.pm). These children are then instantiated in another Perl program.

examples:

#***in file base.pm
package base  

sub new
{
#-- new code here
}

sub bprint()
{
#-- some print code here
}


#***in file child.pm
package child 

use base;
@ISA = qw(base); #so we're a base, and those methods should be 
                 #available to instances of child

sub new
{
#-- new code here
}

sub print
{
#-- some other code here
}

#***in file main.p
use child;

$var = new child; #so far, so good

$var->print(); #still ok

$var->bprint(); #not ok, I get an error stating:
"can't locate object method "bprint" via package "child"

I first tried to access "bprint" from within the child module itself, and then moved it out to the main.p when that didn't work. I thought that the @ISA array would be searched for a package containing a method not defined in the current package, and hence "bprint" would be found? It doesn't seem to recognize that what's in base.pm is a package - I can do whatever I want to that code and not affect the erroneous outcome.

hmmmm, any help greatly appreciated (i've done lots of experimenting, to no avail..)

dora c

 

[Coderifous]

#=========== FILE:  testbase.pm ========
package testbase;

sub base_p {
print "Found the base_p function\n";
}

1;
#=======================================

#========== FILE:  testchild.pm ========
package testchild;
use testbase;
@ISA = qw(testbase);

sub child_p {
print "Found the child_p function\n";
}

1;
#=======================================

After creating those two files, I was able to execute this code:

use testchild;

$j = new testchild;

$j->child_p;
$j->base_p;

And the output is what would be expected:

Found the child_p function
Found the base_p function


Do you see a difference in our code that may prevent yours from functioning?

--jim

 

[MikeLacey]

is base a reserved word? Mike
________________________________________________________________________________

"Experience is the comb that Nature gives us, after we are bald."

Is that a haiku?
I never could get the hang
of writing those things.

 

[DoraC]

"base" a reserved word?
I replaced "base" with "testbase"
and now my code works


dora

 

[Coderifous]

Yea, it is a reserved word (sordof):

http://www.perldoc.com/perl5.6.1/lib/base.html

--jim

 

[19decsat]

hi Coderifous,

when i try your code. and run the program i get this error


Can't locate object method "new" via package "testchild" at newpr.pl line 3.


thanks in advance
19decsat