Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
indirect(3)	      User Contributed Perl Documentation	   indirect(3)

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

       Version 0.39

       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

       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

       This module is not a source filter.

	   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

	   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).

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

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

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

       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 .

   "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.

       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

       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 '' entry from %INC.

       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

       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.

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

       o   <> : 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   <>
	   : 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.

       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).

       Vincent Pit "<>".

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

       Please report any bugs or feature requests to "bug-indirect at", or	through	the web	interface at
       <>.  I will be
       notified, and then you'll automatically be notified of progress on your
       bug as I	make changes.

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

	   perldoc indirect

       Bram, for motivation and	advices.

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

       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 v5.32.1			  2019-07-08			   indirect(3)


Want to link to this manual page? Use this URL:

home | help