indirect

indirect(3pm)         User Contributed Perl Documentation        indirect(3pm)

NAME
       indirect - Lexically warn about using the indirect method call syntax.

VERSION
       Version 0.39

SYNOPSIS
       In a script :

           no indirect;               # lexically enables the pragma
           my $x = new Apple 1, 2, 3; # warns
           {
            use indirect;     # lexically disables the pragma
            my $y = new Pear; # legit, does not warn
            {
             # lexically specify an hook called for each indirect construct
             no indirect hook => sub {
              die "You really wanted $_[0]\->$_[1] at $_[2]:$_[3]"
             };
             my $z = new Pineapple 'fresh'; # croaks 'You really wanted...'
            }
           }
           try { ... }; # warns if try() hasn't been declared in this package

           no indirect 'fatal';     # or ':fatal', 'FATAL', ':Fatal' ...
           if (defied $foo) { ... } # croaks, note the typo

       Global uses :

           # Globally enable the pragma from the command-line
           perl -M-indirect=global -e 'my $x = new Banana;' # warns

           # Globally enforce the pragma each time perl is executed
           export PERL5OPT="-M-indirect=global,fatal"
           perl -e 'my $y = new Coconut;' # croaks

DESCRIPTION
       When enabled, this pragma warns about indirect method calls that are
       present in your code.

       The indirect syntax is now considered harmful, since its parsing has
       many quirks and its use is error prone : when the subroutine "foo" has
       not been declared in the current package, "foo $x" actually compiles to
       "$x->foo", and "foo { key => 1 }" to "'key'->foo(1)".  Please refer to
       the "REFERENCES" section for a more complete list of reasons for
       avoiding this construct.

       This pragma currently does not warn for core functions ("print", "say",
       "exec" or "system").  This may change in the future, or may be added as
       optional features that would be enabled by passing options to
       "unimport".

       This module is not a source filter.

METHODS
   "unimport"
           no indirect;
           no indirect 'fatal';
           no indirect hook => sub { my ($obj, $name, $file, $line) = @_; ... };
           no indirect 'global';
           no indirect 'global, 'fatal';
           no indirect 'global', hook => sub { ... };

       Magically called when "no indirect @opts" is encountered.  Turns the
       module on.  The policy to apply depends on what is first found in @opts
       :

       o   If it is a string that matches "/^:?fatal$/i", the compilation will
           croak when the first indirect method call is found.

           This option is mutually exclusive with the 'hook' option.

       o   If the key/value pair "hook => $hook" comes first, $hook will be
           called for each error with a string representation of the object as
           $_[0], the method name as $_[1], the current file as $_[2] and the
           line number as $_[3].  If and only if the object is actually a
           block, $_[0] is assured to start by '{'.

           This option is mutually exclusive with the 'fatal' option.

       o   If none of "fatal" and "hook" are specified, a warning will be
           emitted for each indirect method call.

       o   If @opts contains a string that matches "/^:?global$/i", the pragma
           will be globally enabled for all code compiled after the current
           "no indirect" statement, except for code that is in the lexical
           scope of "use indirect".  This option may come indifferently before
           or after the "fatal" or "hook" options, in the case they are also
           passed to "unimport".

           The global policy applied is the one resulting of the "fatal" or
           "hook" options, thus defaults to a warning when none of those are
           specified :

               no indirect 'global';                # warn for any indirect call
               no indirect qw<global fatal>;        # die on any indirect call
               no indirect 'global', hook => \&hook # custom global action

           Note that if another policy is installed by a "no indirect"
           statement further in the code, it will overrule the global policy :

               no indirect 'global';  # warn globally
               {
                no indirect 'fatal';  # throw exceptions for this lexical scope
                ...
                require Some::Module; # the global policy will apply for the
                                      # compilation phase of this module
               }

   "import"
           use indirect;

       Magically called at each "use indirect". Turns the module off.

       As explained in "unimport"'s description, an "use indirect" statement
       will lexically override a global policy previously installed by "no
       indirect 'global', ..." (if there's one).

FUNCTIONS
   "msg"
           my $msg = msg($object, $method, $file, $line);

       Returns the default error message that "indirect" generates when an
       indirect method call is reported.

CONSTANTS
   "I_THREADSAFE"
       True iff the module could have been built with thread-safety features
       enabled.

   "I_FORKSAFE"
       True iff this module could have been built with fork-safety features
       enabled.  This will always be true except on Windows where it's false
       for perl 5.10.0 and below .

DIAGNOSTICS
   "Indirect call of method "%s" on object "%s" at %s line %d."
       The default warning/exception message thrown when an indirect method
       call on an object is found.

   "Indirect call of method "%s" on a block at %s line %d."
       The default warning/exception message thrown when an indirect method
       call on a block is found.

ENVIRONMENT
   "PERL_INDIRECT_PM_DISABLE"
       If this environment variable is set to true when the pragma is used for
       the first time, the XS code won't be loaded and, although the
       'indirect' lexical hint will be set to true in the scope of use, the
       pragma itself won't do anything.  In this case, the pragma will always
       be considered to be thread-safe, and as such "I_THREADSAFE" will be
       true.  This is useful for disabling "indirect" in production
       environments.

       Note that clearing this variable after "indirect" was loaded has no
       effect.  If you want to re-enable the pragma later, you also need to
       reload it by deleting the 'indirect.pm' entry from %INC.

CAVEATS
       The implementation was tweaked to work around several limitations of
       vanilla "perl" pragmas : it's thread safe, and does not suffer from a
       "perl 5.8.x-5.10.0" bug that causes all pragmas to propagate into
       "require"d scopes.

       Before "perl" 5.12, "meth $obj" (no semicolon) at the end of a file is
       not seen as an indirect method call, although it is as soon as there is
       another token before the end (as in "meth $obj;" or "meth $obj 1").  If
       you use "perl" 5.12 or greater, those constructs are correctly
       reported.

       With 5.8 perls, the pragma does not propagate into "eval STRING".  This
       is due to a shortcoming in the way perl handles the hints hash, which
       is addressed in perl 5.10.

       The search for indirect method calls happens before constant folding.
       Hence "my $x = new Class if 0" will be caught.

REFERENCES
       Numerous articles have been written about the quirks of the indirect
       object construct :

       o   <http://markmail.org/message/o7d5sxnydya7bwvv> : Far More Than
           Everything You've Ever Wanted to Know about the Indirect Object
           syntax, Tom Christiansen, 1998-01-28.

           This historical post to the "perl5-porters" mailing list raised
           awareness about the perils of this syntax.

       o   <http://www.shadowcat.co.uk/blog/matt-s-trout/indirect-but-still-fatal>
           : Indirect but still fatal, Matt S. Trout, 2009-07-29.

           In this blog post, the author gives an example of an undesirable
           indirect method call on a block that causes a particularly
           bewildering error.

DEPENDENCIES
       perl 5.8.1.

       A C compiler.  This module may happen to build with a C++ compiler as
       well, but don't rely on it, as no guarantee is made in this regard.

       Carp (standard since perl 5), XSLoader (since perl 5.6.0).

AUTHOR
       Vincent Pit "<vpit@cpan.org>".

       You can contact me by mail or on "irc.perl.org" (vincent).

BUGS
       Please report any bugs or feature requests to "bug-indirect at
       rt.cpan.org", or through the web interface at
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=indirect>.  I will be
       notified, and then you'll automatically be notified of progress on your
       bug as I make changes.

SUPPORT
       You can find documentation for this module with the perldoc command.

           perldoc indirect

ACKNOWLEDGEMENTS
       Bram, for motivation and advices.

       Andrew Main and Florian Ragwitz, for testing on real-life code and
       reporting issues.

COPYRIGHT & LICENSE
       Copyright 2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2019
       Vincent Pit, all rights reserved.

       This program is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl v5.30.0                      2019-10-19                     indirect(3pm)