A Matter of (Indirect) Syntax - Page 171

Thus far we've called object methods using the arrow, or ->, syntax. While popular and attractive, you may sometimes see scripts or documentation that uses indirect object syntax. One of the more common examples is the indirect constructor, for example when creating a CGI object:

my $cgiobj = new CGI;

This indirect syntax specifies the method name first, followed by the class or object name, and finally any parameter list if available. Using the indirect syntax, we could replace our earlier call to header(-expires=>'-1d') with:

print STDOUT header $cgiobj (expires=>'-1d');

In one sense, the indirect syntax is just that: indirect, and thus less clear. Why would anyone prefer the above? But here's a neat trick — using the indirect syntax, you can substitute an expression for the class or method name. In doing do, you can in fact both create and use the object in a single statement:

print STDOUT header {new CGI} (expires=>'-1d');

Most of the time, the parentheses can be omitted from the parameter list when using indirect syntax, but at the peril of further obtuseness. While this author generally endorses the arrow, rather than indirect, syntax, there are times when indirect is indeed more intuitive, such as with the new object constructor.

Black Box Restated

There isn't much to it — using objects, that is. And that's the whole point of the little black box, so long as you know how to pull its levers and twiddle its knobs. Many Web developers may never create object classes themselves, but will likely use them as created by others, and propagated as Perl modules. In practice, this is the most important skill, along with understanding just why object orientation is so useful (points we covered early on).

Still, the thirsty and inquisitive minds of Perl developers may hunger for more. It's not enough to learn how to drive the car — we want to know how to build a car! Creating classes and objects is, of course, slightly more complicated than using them, but no less fulfilling. Next time we look at object orientation in Perl, we'll go under the hood, as it were, and begin building object classes of our own, for both our own enjoyment and the enjoyment of others.

Classism - Page 170
The Perl You Need to Know