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Man Pages


Manual Reference Pages  -  INDIRECT (3)

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NAME

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

CONTENTS

VERSION

Version 0.33

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() hasnt 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). In <http://www.shadowcat.co.uk/blog/matt-s-trout/indirect-but-still-fatal>, Matt S. Trout gives an example of an undesirable indirect method call on a block that can cause a particularly bewildering error.

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 <B>notB> a source filter.

METHODS

CWunimport



    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 <B>allB> 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
    }



CWimport



    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

CWmsg



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



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

CONSTANTS

CWI_THREADSAFE

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

CWI_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

CWIndirect 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.

CWIndirect 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

CWPERL_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 required 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.

Indirect constructs that appear in code eval’d during the global destruction phase of a spawned thread or pseudo-fork (the processes used internally for the fork emulation on Windows) are not reported.

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

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



Tests code coverage report is available at <http://www.profvince.com/perl/cover/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 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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perl v5.20.3 INDIRECT (3) 2014-09-29

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