indirect(3pm)


NAME

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

VERSION

   Version 0.37

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
   :

   *   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.

   *   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.

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

   *   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 :

   *   <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.

   *   <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, "<perl at profvince.com>", <http://www.profvince.com>.

   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 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.





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