1NAME
2 indirect - Lexically warn about using the indirect method call syntax.
3
4VERSION
5 Version 0.39
6
7SYNOPSIS
8 In a script :
9
10 no indirect; # lexically enables the pragma
11 my $x = new Apple 1, 2, 3; # warns
12 {
13 use indirect; # lexically disables the pragma
14 my $y = new Pear; # legit, does not warn
15 {
16 # lexically specify an hook called for each indirect construct
17 no indirect hook => sub {
18 die "You really wanted $_[0]\->$_[1] at $_[2]:$_[3]"
19 };
20 my $z = new Pineapple 'fresh'; # croaks 'You really wanted...'
21 }
22 }
23 try { ... }; # warns if try() hasn't been declared in this package
24
25 no indirect 'fatal'; # or ':fatal', 'FATAL', ':Fatal' ...
26 if (defied $foo) { ... } # croaks, note the typo
27
28 Global uses :
29
30 # Globally enable the pragma from the command-line
31 perl -M-indirect=global -e 'my $x = new Banana;' # warns
32
33 # Globally enforce the pragma each time perl is executed
34 export PERL5OPT="-M-indirect=global,fatal"
35 perl -e 'my $y = new Coconut;' # croaks
36
37DESCRIPTION
38 When enabled, this pragma warns about indirect method calls that are
39 present in your code.
40
41 The indirect syntax is now considered harmful, since its parsing has
42 many quirks and its use is error prone : when the subroutine "foo" has
43 not been declared in the current package, "foo $x" actually compiles to
44 "$x->foo", and "foo { key => 1 }" to "'key'->foo(1)". Please refer to
45 the "REFERENCES" section for a more complete list of reasons for
46 avoiding this construct.
47
48 This pragma currently does not warn for core functions ("print", "say",
49 "exec" or "system"). This may change in the future, or may be added as
50 optional features that would be enabled by passing options to
51 "unimport".
52
53 This module is not a source filter.
54
55METHODS
56 "unimport"
57 no indirect;
58 no indirect 'fatal';
59 no indirect hook => sub { my ($obj, $name, $file, $line) = @_; ... };
60 no indirect 'global';
61 no indirect 'global, 'fatal';
62 no indirect 'global', hook => sub { ... };
63
64 Magically called when "no indirect @opts" is encountered. Turns the
65 module on. The policy to apply depends on what is first found in @opts :
66
67 * If it is a string that matches "/^:?fatal$/i", the compilation will
68 croak when the first indirect method call is found.
69
70 This option is mutually exclusive with the 'hook' option.
71
72 * If the key/value pair "hook => $hook" comes first, $hook will be
73 called for each error with a string representation of the object as
74 $_[0], the method name as $_[1], the current file as $_[2] and the
75 line number as $_[3]. If and only if the object is actually a block,
76 $_[0] is assured to start by '{'.
77
78 This option is mutually exclusive with the 'fatal' option.
79
80 * If none of "fatal" and "hook" are specified, a warning will be
81 emitted for each indirect method call.
82
83 * If @opts contains a string that matches "/^:?global$/i", the pragma
84 will be globally enabled for all code compiled after the current "no
85 indirect" statement, except for code that is in the lexical scope of
86 "use indirect". This option may come indifferently before or after
87 the "fatal" or "hook" options, in the case they are also passed to
88 "unimport".
89
90 The global policy applied is the one resulting of the "fatal" or
91 "hook" options, thus defaults to a warning when none of those are
92 specified :
93
94 no indirect 'global'; # warn for any indirect call
95 no indirect qw<global fatal>; # die on any indirect call
96 no indirect 'global', hook => \&hook # custom global action
97
98 Note that if another policy is installed by a "no indirect"
99 statement further in the code, it will overrule the global policy :
100
101 no indirect 'global'; # warn globally
102 {
103 no indirect 'fatal'; # throw exceptions for this lexical scope
104 ...
105 require Some::Module; # the global policy will apply for the
106 # compilation phase of this module
107 }
108
109 "import"
110 use indirect;
111
112 Magically called at each "use indirect". Turns the module off.
113
114 As explained in "unimport"'s description, an "use indirect" statement
115 will lexically override a global policy previously installed by "no
116 indirect 'global', ..." (if there's one).
117
118FUNCTIONS
119 "msg"
120 my $msg = msg($object, $method, $file, $line);
121
122 Returns the default error message that "indirect" generates when an
123 indirect method call is reported.
124
125CONSTANTS
126 "I_THREADSAFE"
127 True iff the module could have been built with thread-safety features
128 enabled.
129
130 "I_FORKSAFE"
131 True iff this module could have been built with fork-safety features
132 enabled. This will always be true except on Windows where it's false for
133 perl 5.10.0 and below .
134
135DIAGNOSTICS
136 "Indirect call of method "%s" on object "%s" at %s line %d."
137 The default warning/exception message thrown when an indirect method
138 call on an object is found.
139
140 "Indirect call of method "%s" on a block at %s line %d."
141 The default warning/exception message thrown when an indirect method
142 call on a block is found.
143
144ENVIRONMENT
145 "PERL_INDIRECT_PM_DISABLE"
146 If this environment variable is set to true when the pragma is used for
147 the first time, the XS code won't be loaded and, although the 'indirect'
148 lexical hint will be set to true in the scope of use, the pragma itself
149 won't do anything. In this case, the pragma will always be considered to
150 be thread-safe, and as such "I_THREADSAFE" will be true. This is useful
151 for disabling "indirect" in production environments.
152
153 Note that clearing this variable after "indirect" was loaded has no
154 effect. If you want to re-enable the pragma later, you also need to
155 reload it by deleting the 'indirect.pm' entry from %INC.
156
157CAVEATS
158 The implementation was tweaked to work around several limitations of
159 vanilla "perl" pragmas : it's thread safe, and does not suffer from a
160 "perl 5.8.x-5.10.0" bug that causes all pragmas to propagate into
161 "require"d scopes.
162
163 Before "perl" 5.12, "meth $obj" (no semicolon) at the end of a file is
164 not seen as an indirect method call, although it is as soon as there is
165 another token before the end (as in "meth $obj;" or "meth $obj 1"). If
166 you use "perl" 5.12 or greater, those constructs are correctly reported.
167
168 With 5.8 perls, the pragma does not propagate into "eval STRING". This
169 is due to a shortcoming in the way perl handles the hints hash, which is
170 addressed in perl 5.10.
171
172 The search for indirect method calls happens before constant folding.
173 Hence "my $x = new Class if 0" will be caught.
174
175REFERENCES
176 Numerous articles have been written about the quirks of the indirect
177 object construct :
178
179 * <http://markmail.org/message/o7d5sxnydya7bwvv> : Far More Than
180 Everything You've Ever Wanted to Know about the Indirect Object
181 syntax, Tom Christiansen, 1998-01-28.
182
183 This historical post to the "perl5-porters" mailing list raised
184 awareness about the perils of this syntax.
185
186 * <http://www.shadowcat.co.uk/blog/matt-s-trout/indirect-but-still-fat
187 al> : Indirect but still fatal, Matt S. Trout, 2009-07-29.
188
189 In this blog post, the author gives an example of an undesirable
190 indirect method call on a block that causes a particularly
191 bewildering error.
192
193DEPENDENCIES
194 perl 5.8.1.
195
196 A C compiler. This module may happen to build with a C++ compiler as
197 well, but don't rely on it, as no guarantee is made in this regard.
198
199 Carp (standard since perl 5), XSLoader (since perl 5.6.0).
200
201AUTHOR
202 Vincent Pit "<vpit@cpan.org>".
203
204 You can contact me by mail or on "irc.perl.org" (vincent).
205
206BUGS
207 Please report any bugs or feature requests to "bug-indirect at
208 rt.cpan.org", or through the web interface at
209 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=indirect>. I will be
210 notified, and then you'll automatically be notified of progress on your
211 bug as I make changes.
212
213SUPPORT
214 You can find documentation for this module with the perldoc command.
215
216 perldoc indirect
217
218ACKNOWLEDGEMENTS
219 Bram, for motivation and advices.
220
221 Andrew Main and Florian Ragwitz, for testing on real-life code and
222 reporting issues.
223
224COPYRIGHT & LICENSE
225 Copyright 2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2019 Vincent
226 Pit, all rights reserved.
227
228 This program is free software; you can redistribute it and/or modify it
229 under the same terms as Perl itself.
230
231