README
1Readonly version 1.03
2=====================
3
4CHANGES FROM VERSION 1.02 (See "Changes" file for details)
5
6o Syntax of Readonly() function has changed, for users of
7 Perl 5.8 and later.
8
9
10DESCRIPTION
11
12Readonly.pm provides a facility for creating non-modifiable scalars,
13arrays, and hashes.
14
15Perl provides a built-in mechanism (the "use constant" pragma) to
16create constant scalars and lists. That mechanism has several
17limitations, however:
18
19 It creates only scalars and arrays (not hashes).
20 It creates "variables" that have no leading $ or @ character.
21 The variables it creates cannot be interpolated into strings.
22 It works only at compile time.
23 The variables it creates are global, never lexical.
24 Sometimes you have to be careful with your syntax when using them
25 (for example, when using one as a hash key).
26 You can't pass these constants around like variables (for example,
27 you can't take references to them).
28 It is rather difficult to make and use complex data structures with
29 use constant.
30 "use constant" directives can be overridden by subsequent "use
31 constant" directives. (this does generate a warning).
32
33Readonly.pm, by contrast:
34
35 Creates scalars, arrays (not lists), and hashes.
36 Creates variables that look and work like native perl variables.
37 Creates global or lexical variables.
38 Works at runtime or compile time.
39 Works with deep or shallow data structures.
40 Prevents reassignment of Readonly variables.
41
42EXAMPLES OF USE
43
44 Readonly::Scalar $x => "A string value";
45 Readonly::Array @x => (1, 2, 3, 4);
46 Readonly::Hash %x => (key1 => 'value1', key2 => 'value2');
47
48If the program subsequently tries to modify $x, @x, or %x, the program
49will die with an error message.
50
51Deep structures are a breeze:
52
53 Readonly::Hash %x => {key1 => [1, 2], key2 => [3, 4, 5]};
54 print $x{key1}[1];
55
56Try that with "use constant"!
57
58INSTALLATION
59
60To install this module, do the standard Perl module four-step:
61
62 perl Makefile.PL or perl Makefile.pl LIB='my/install/path'
63 make
64 make test
65 make install
66
67
68DEPENDENCIES
69
70Test::Harness and Test::More, if you want to run the test suites (and
71yes, you should). Also, Carp.pm and Exporter.pm, but they come with
72Perl.
73
74Readonly::XS (available on CPAN) is a companion module to Readonly.
75If that module is present, Readonly will use it for handling scalars.
76This results in a significant speed improvement. This is transparent
77to your code; whether or not the XS module is present, Readonly works
78the same.
79
80
81COPYRIGHT AND LICENSE
82
83Eric J. Roode, roode@cpan.org
84
85Copyright (c) 2001-2004 by Eric J. Roode. All Rights Reserved. This module
86is free software; you can redistribute it and/or modify it under the
87same terms as Perl itself.
88
89If you have suggestions for improvement, please drop me a line. If
90you make improvements to this software, I ask that you please send me
91a copy of your changes. Thanks.
92