What are COM objects?

So how does COM allow you to perform this magic?

When you break them down to their essences, all objects do the same basic things no matter what languages they are written in. Specifically, all objects have methods and properties that define how they work internally.

Further, all objects expose a set of "public" methods that allow objects in the outside world to interact with them.

Finally, it is often the case that methods accept a set of incoming parameters that modify the behavior of the method, and return some type of output to the caller of the method.

Usually, every programming language will implement these basic characteristics, but will do so in slightly different ways. For example, consider the same add() method defined first in Java and then in Perl:

public int add(int a, int b) {
    return a+b;
}

sub add {
    my $a = shift;
    my $b = shift;
    return $a + $b;
}

Quite different, eh? That's why it is so hard for languages to interact.

The beauty of COM is that it defines a language-independent specification that abstracts out these basic object properties.

COM is a protocol that defines a standard way for objects to speak to one another, regardless of the specific way in which they actually implement methods and properties.

More specifically, COM is a specification that defines how to call methods on objects.

Introduction to Perl on Windows: Writing COM Components in Perl
Introduction to Perl on Windows - Table of Contents
The IDL