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overloading operators
More Objects example from a Well House Consultants training course
More on More Objects [link]
Source code: pover Module: P218
# overloading operators
{ package box; # Define which functions are to run when certain operators # are called on am object of type box. use overload '==' => "same", '*' => "pyle", '""' => formatter, '+' => "stackem"; # Constructor - nothing special here sub new { my ($class,$x,$y,$z) = @_; my %info; $info{x} = $x; $info{y} = $y; $info{z} = $z; bless \%info,$class; } # A method that will be used in the standard Perl way # again, nothing special here sub volume { my $self = shift; $$self{x} * $$self{y} * $$self{z}; } # The method that is to be used when the + operator is used # Takes two objects as parameters and return a third new object sub stackem { my $this = shift; my $that = shift; return new box( ($$this{x}>$$that{x}) ? $$this{x} : $$that{x}, ($$this{y}>$$that{y}) ? $$this{y} : $$that{y}, $$this{z} + $$that{z} ); } # The method that is to be used when the * operator is used # Takes two parameters. This is set up so that a multiplication # takes a box object as the left parameter, and a numeric value # to the right sub pyle { my ($this,$that) = @_; return new box( $$this{x}, $$this{y}, $$this{z} * $that); } # Equality testing. Does not need to check if things are identical. # In this example, checks if the two objects have the same volume. sub same { my ($this,$that) = @_; $va = $this->volume(); $vb = $that->volume(); $va == $vb; } # What to do when printing out an object variables / expanding it # within a double quoted string sub formatter { my ($this) = @_; $$this{x} . " by " . $$this{y} . " by " . $$this{z} ; } } # Test program to demonstrate the above $first = new box(10,20,15); $second = new box(20,15,10); $third = $first + $second; # Note that * uses the class code above, but the + is in # an integer context and does a simple, normal addtion: $fourth = $first * (2 + 3); print ($first->volume(),"\n"); print ($second->volume(),"\n"); print ($third->volume(),"\n"); print ($fourth->volume(),"\n"); if ($first == $second) { print "first and second same (in volume)\n"; } else { print "Different volumes - first and second\n"; } if ($first == $third) { print "first and third same (in volume)\n"; } else { print "Different volumes - first and third\n"; } print ("$first is an example\n"); __END__ How it runs: munchkin:j11pl grahamellis$ perl pover 3000 3000 10000 15000 first and second same (in volume) Different volumes - first and third 10 by 20 by 15 is an example munchkin:j11pl grahamellis$ Learn about this subject
This module and example are covered on the following public courses:
* Perl Programming * Perl for Larger Projects * Learning to program in Perl * Perl Programming Also available on on site courses for larger groups Books covering this topic
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