Reference Variables and Type Globbing
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Hard References
Hard references refer to an actual value or some other chunk of
data. You may think of them in the C++ sense, in that, they can only
exist if they refer to another variable. Some examples are:
<![CDATA[
$scalar_reference = \$value;
$const_reference = \3.1415;
$array_reference = \@list_of_some_kind;
$hash_reference = \%table;
$code_reference = \&interrupt_handler;
$glob_reference = \*DATA_FILE;
]]>
The backslash operator "\" is similar to the address-of
operator (&) in C/C++.
Using Hard References
To access hard references, you treat $reference_name as
the variable name and use the appropriate variable symbol (ie,
$, @, % or &) to
dereference it, as in:
<![CDATA[
print "scalar value = $$scalar_reference\n";
print "array values = @$array_reference\n";
print "hash keys and values = %$hash_reference\n";
$a = $$array_reference[3]; # access 4th element
# yet another way to access the 4th element
$a = ${array_reference}[3];
]]>
Symbolic References
If a variable is not a reference to another variable and you
dereference it, then you have a symbolic reference, such as:
<![CDATA[
$sym = 'width';
$$sym = 100; # sets $width to 100
$$sym[3] = 20; # sets $width[3] to 20
$sym->[3] = 20; # same
&$sym(); # call &width()
]]>
Restricting Symbolic Reference Use
To restrict the use of symbolic references, you can do:
<![CDATA[
use strict 'refs';
]]>
and then only hard references will be allowed for the rest of the
block. To reset (allow) the use of symbolic references afterward, do:
<![CDATA[
no strict 'refs';
]]>
Type Globbing
Typeglobs, represented by an asterisk (*), is a a way to represent all
types. With the introduction of references, typeglobs are now only
used to reference file handles.
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Last Modified: $Date: 1997/09/18 08:38:04 $