1deprecate(3pm) Perl Programmers Reference Guide deprecate(3pm)
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6 deprecate - Perl pragma for deprecating the inclusion of a module in
7 core
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10 use deprecate; # warn about future absence if loaded from core
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13 This pragma simplifies the maintenance of dual-life modules that will
14 no longer be included in the Perl core in a future Perl release, but
15 are still included currently.
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17 The purpose of the pragma is to alert users to the status of such a
18 module by issuing a warning that encourages them to install the module
19 from CPAN, so that a future upgrade to a perl which omits the module
20 will not break their code.
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22 This warning will only be issued if the module was loaded from a core
23 library directory, which allows the "use deprecate" line to be included
24 in the CPAN version of the module. Because the pragma remains silent
25 when the module is run from a non-core library directory, the pragma
26 call does not need to be patched into or out of either the core or CPAN
27 version of the module. The exact same code can be shipped for either
28 purpose.
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30 Important Caveat
31 Note that when a module installs from CPAN to a core library directory
32 rather than the site library directories, the user gains no protection
33 from having installed it.
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35 At the same time, this pragma cannot detect when such a module has
36 installed from CPAN to the core library, and so it would endlessly and
37 uselessly exhort the user to upgrade.
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39 Therefore modules that can install from CPAN to the core library must
40 make sure not to call this pragma when they have done so. Generally
41 this means that the exact logic from the installer must be mirrored
42 inside the module. E.g.:
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44 # Makefile.PL
45 WriteMakefile(
46 # ...
47 INSTALLDIRS => ( "$]" >= 5.011 ? 'site' : 'perl' ),
48 );
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50 # lib/Foo/Bar.pm
51 use if "$]" >= 5.011, 'deprecate';
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53 (The above example shows the most important case of this: when the
54 target is a Perl older than 5.12 (where the core library directories
55 take precedence over the site library directories) and the module being
56 installed was included in core in that Perl version. Under those
57 circumstances, an upgrade of the module from CPAN is only possible by
58 installing to the core library.)
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61 None by default. The only method is "import", called by "use
62 deprecate;".
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65 First example to "use deprecate;" was Switch.
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68 Original version by Nicholas Clark
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71 Copyright (C) 2009, 2011
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73 This library is free software; you can redistribute it and/or modify it
74 under the same terms as Perl itself, either Perl version 5.10.0 or, at
75 your option, any later version of Perl 5 you may have available.
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79perl v5.36.0 2022-08-30 deprecate(3pm)