This section provides a tutorial example on how to invoke a package subroutine as an object method. $object->subroutine(...) is most commonly used syntax of calling object methods.
In the previous section, we learned how to convert a hard reference to an object of a specific package.
Now let's see how to invoke package subroutines as object methods.
Similar to class method invocation, if a subroutine is invoked as an object
method, the object (blessed reference) will be automatically inserted into
the argument list as the first argument.
There are two ways to invoke a subroutine as an object method:
1. Using the "indirect object" syntax:
sub_identifier $object arg2, arg3, ...
where "sub_identifier" is the subroutine identifier without any package name prefixes
and "&";
"$object" is a blessed object; and
"arg2, arg3, ..." is the argument list
starting from the second argument without parentheses.
2. Using the "->" notation:
$object->sub_identifier(arg2, arg3, ...)
where "sub_identifier" is the subroutine identifier without any package name prefixes
and "&";
"$object" is a blessed object; and "arg2, arg3, ..." is the argument list
starting from the second argument. In this format, parentheses on the argument
list are optional.
I used both syntaxes in the following tutorial program, ObjectMethodTest.pl:
#- ObjectMethodTest.pl
#- Copyright (c) 1999 by Dr. Herong Yang, http://www.herongyang.com/
#
package Foo;
sub echoParam {
$i = 0;
while ( $p = shift) {
$i++;
print(" Param #",$i," = ",$p,"\n");
}
}
package main;
$m = "Hello world!";
$r = \$m;
$x = bless($r,Foo);
print("\nCheck data types:\n");
print(" Type of \$n: ",ref($n),"\n");
print(" Type of \$r: ",ref($r),"\n");
print(" Type of \$x: ",ref($x),"\n");
print(" \$x == \$r\n") if ($x==$r);
print("\nTest 1:\n");
echoParam $x "Fire", "Water";
# print("\nTest 2:\n");
# &echoParam $x "Fire", "Water";
# print("\nTest 3:\n");
# echoParam $m "Fire", "Water";
print("\nTest 4:\n");
$x->echoParam("Java", "Perl");
exit;
Here is the output of the tutorial program:
Check data types:
Type of $n:
Type of $r: Foo
Type of $x: Foo
$x == $r
Test 1:
Param #1 = Foo=SCALAR(0x1ab2f54)
Param #2 = Fire
Param #3 = Water
Test 4:
Param #1 = Foo=SCALAR(0x1ab2f54)
Param #2 = Java
Param #3 = Perl
Note that:
It is true that you can bless any reference into an object.
In my sample program, I blessed a reference of the scalar into
an object of class "Foo".
Tests 1 and 4 are special ways to invoke a subroutine as an object method.
