The regular program, ex9.pl, sets up an array of record-like structures. The Constructor for this class calls the method new, which establishes a reference to an object of the class type. The function new then calls initialize which either assigns initial values that were passed as parameters, or else assigns default values. Later, elements in the array are modified using the method Modify, or printed using PrintRec.
The typical output one would expect is printed in red. A few additonal lines of output, printed in blue, are used to better understand what is happening in the Perl Module. Such debugging output would not normally appear in the final program.
package Student; # Class Definition for Object of type Student
@student_data = qw(Name ID GPA ); # Name the fields
### The subroutines "new" and "initialize" for the Constructor
sub new
{
print "new: @_ \n";
my $class_name = shift; # Gets class name from parmlist
my $recref = {}; # Creates reference to object
bless $recref, $class_name; # Associates reference with class
$recref -> initialize(@_); # Call local initialize subroutine
# passing rest of parmlist
return $recref; # Explicit return of value of $recref
}
sub initialize
{
print "initialize: @_ \n";
my $stu_ref = shift; # Receive an object reference as 1st param
my %parms = @_; # Get passed parameters from the call to "new"
# Change hash reference for key with supplied value, or assign default
$stu_ref -> {'Name'} = $parms{'Name'} || "NOBODY";
$stu_ref -> {'ID'} = $parms{'ID'} || "NO_ID";
$stu_ref -> {'GPA'} = $parms{'GPA'} || 0;
}
sub PrintRec # Print a student record
{
print "PrintRec: @_ \n";
my $instance = shift; # Figure out who I am
for(@student_data) # Go through all fields
{
print "$_: ", $instance -> {$_}, "\n"; # Print key and value
}
}
sub Modify # Modify student Record
{
print "Modify: @_ \n";
my $instance = shift; # Figure out who I am
my %parms = @_; # Make hash out of rest of parm list
# Step through all keys in parm list
for(keys %parms)
{
$instance -> {$_} = $parms{$_}; # Replace with new value
}
}
1; # Return 1 to say Perl Module loaded correctly
The Program: ex9.pl
#!/usr/bin/perl -w
### This program deals with an array of records. The records are objects
### of type Student, which are defined in Perl Module called StudentRec.pm
require StudentRec; # Allows program to use items defined in Perl Module
### subroutine to print out records in an Array
sub print_kids
{
my $kid;
foreach $kid (@person)
{
PrintRec $kid; # Call method "PrintRec" defined for class Student
print "\n";
}
}
#### Initialize Array of Records ####
## Method "new" creates an object of type Student, and then passes
## parameters onto an initialization routine. One would usually
## initialize from a file rather than direct assignment, however.
# This Record is defined in typical order (Name, ID, GPA)
$person[0] = new Student( 'Name' => "Bill",
'ID' => "12-345-6",
'GPA' => 3.8);
# No fields are defined for this record - Constructor uses defaults
$person[1] = new Student;
# Fields may be defined in any order since the record is a hash
$person[2] = new Student( 'GPA' => 4.0,
'Name' => "Hillary",
'ID' => "98-765-4");
# Print out details print "Before...\n"; print_kids;
#### Change things a bit ####
# Add new person. Undefined fields take the default values
$person[3] = new Student('Name' => "Monica");
# Call Modify method in package
$person[0] -> Modify('GPA' => 1.6); # Pass key and value in parm list
print "After...\n"; print_kids;