The symbol table for a package happens to be stored in the hash of that
name with two colons appended. The main symbol table's name is thus
-C<%main::>, or C<%::> for short. Likewise symbol table for the nested
+C<%main::>, or C<%::> for short. Likewise the symbol table for the nested
package mentioned earlier is named C<%OUTER::INNER::>.
The value in each entry of the hash is what you are referring to when you
local $main::{foo} = $main::{bar};
You can use this to print out all the variables in a package, for
-instance. The standard but antequated F<dumpvar.pl> library and
+instance. The standard but antiquated F<dumpvar.pl> library and
the CPAN module Devel::Symdump make use of this.
Assignment to a typeglob performs an aliasing operation, i.e.,
@richard and @dick as separate arrays. Tricky, eh?
This mechanism may be used to pass and return cheap references
-into or from subroutines if you won't want to copy the whole
+into or from subroutines if you don't want to copy the whole
thing. It only works when assigning to dynamic variables, not
lexicals.
On return, the reference will overwrite the hash slot in the
symbol table specified by the *some_hash typeglob. This
is a somewhat tricky way of passing around references cheaply
-when you won't want to have to remember to dereference variables
+when you don't want to have to remember to dereference variables
explicitly.
Another use of symbol tables is for making "constant" scalars.
Now you cannot alter $PI, which is probably a good thing all in all.
This isn't the same as a constant subroutine, which is subject to
-optimization at compile-time. This isn't. A constant subroutine is one
-prototyped to take no arguments and to return a constant expression.
-See L<perlsub> for details on these. The C<use constant> pragma is a
+optimization at compile-time. A constant subroutine is one prototyped
+to take no arguments and to return a constant expression. See
+L<perlsub> for details on these. The C<use constant> pragma is a
convenient shorthand for these.
You can say C<*foo{PACKAGE}> and C<*foo{NAME}> to find out what name and
You gave me bar::baz
The C<*foo{THING}> notation can also be used to obtain references to the
-individual elements of *foo, see L<perlref>.
+individual elements of *foo. See L<perlref>.
Subroutine definitions (and declarations, for that matter) need
not necessarily be situated in the package whose symbol table they
(if you can).) You may have multiple C<END> blocks within a file--they
will execute in reverse order of definition; that is: last in, first
out (LIFO). C<END> blocks are not executed when you run perl with the
-C<-c> switch.
+C<-c> switch, or if compilation fails.
Inside an C<END> subroutine, C<$?> contains the value that the program is
going to pass to C<exit()>. You can modify C<$?> to change the exit
suite to save the compiled state of the program.
When you use the B<-n> and B<-p> switches to Perl, C<BEGIN> and
-C<END> work just as they do in B<awk>, as a degenerate case. As currently
-implemented (and subject to change, since its inconvenient at best),
-both C<BEGIN> and<END> blocks are run when you use the B<-c> switch
-for a compile-only syntax check, although your main code is not.
+C<END> work just as they do in B<awk>, as a degenerate case.
+Both C<BEGIN> and C<CHECK> blocks are run when you use the B<-c>
+switch for a compile-only syntax check, although your main code
+is not.
=head2 Perl Classes
=head2 Perl Modules
-A module is just a set of related function in a library file a Perl
-package with the same name as the file. It is specifically designed
-to be reusable by other modules or programs. It may do this by
-providing a mechanism for exporting some of its symbols into the
+A module is just a set of related functions in a library file, i.e.,
+a Perl package with the same name as the file. It is specifically
+designed to be reusable by other modules or programs. It may do this
+by providing a mechanism for exporting some of its symbols into the
symbol table of any package using it. Or it may function as a class
definition and make its semantics available implicitly through
method calls on the class and its objects, without explicitly
-exportating anything. Or it can do a little of both.
+exporting anything. Or it can do a little of both.
For example, to start a traditional, non-OO module called Some::Module,
create a file called F<Some/Module.pm> and start with this template:
Perl packages may be nested inside other package names, so we can have
package names containing C<::>. But if we used that package name
-directly as a filename it would makes for unwieldy or impossible
+directly as a filename it would make for unwieldy or impossible
filenames on some systems. Therefore, if a module's name is, say,
C<Text::Soundex>, then its definition is actually found in the library
file F<Text/Soundex.pm>.
Perl modules always have a F<.pm> file, but there may also be
dynamically linked executables (often ending in F<.so>) or autoloaded
-subroutine definitions (often ending in F<.al> associated with the
+subroutine definitions (often ending in F<.al>) associated with the
module. If so, these will be entirely transparent to the user of
the module. It is the responsibility of the F<.pm> file to load
(or arrange to autoload) any additional functionality. For example,
although the POSIX module happens to do both dynamic loading and
-autoloading, but the user can say just C<use POSIX> to get it all.
+autoloading, the user can say just C<use POSIX> to get it all.
=head1 SEE ALSO
projects / p5sagit/p5-mst-13.2.git / blobdiff