Learning Perl Objects, References amp;amp; Modules [Electronic resources] نسخه متنی

12.3 Sample Object-Oriented Interface: File::Spec

Contrast the subroutines imported by
File::Basename with what another core (non-CPAN)
module has by looking at File::Spec. The
File::Spec module is designed to support
operations commonly performed on file specifications. (A file
specification is usually a file or directory name, but it may be a
name of a file that doesn't existin which
case, it's not really a filename, is it?)

Unlike the File::Basename module, the
File::Spec module has a primarily object-oriented
interface. Saying:

use File::Spec;

in your program imports no
subroutines into the current package. Instead,
you're expected to access the functionality of the
module using class methods:

my $filespec = File::Spec->catfile( $homedir{gilligan},
'web_docs', 'photos', 'USS_Minnow.gif' );

This calls the class method
catfile of the File::Spec
class, building a path appropriate for the local operating system,
and returns a single string.[6] This is similar in syntax to the nearly two dozen other
operations provided by File::Spec:
they're all called as class methods. No instances
are ever created.

[6] That string might be
something like
/home/gilligan/web_docs/photos/USS_Minnow.gif on a
Unix system. On a Windows system, it would typically use backslashes
as directory separators. As you can see, this module lets you write
portable code easily, at least where file specs are concerned.

While it is never stated in
the documentation, perhaps the purpose of creating these as class
methods rather than as imported subroutines is to free the user of
the module from having to worry about namespace collisions (as you
saw for dirname in the previous section). The idea
of an object class without objects, however, seems a bit off kilter.
Perhaps, that's why the module's
author also provides a more traditional interface with:

use File::Spec::Functions qw(catfile curdir);

in which two of the File::Spec's
many functions are imported as ordinary callable subroutines:

my $filespec = catfile( $homedir{gilligan},
'web_docs', 'photos', 'USS_Minnow.gif' );