2 Scope::Upper - Act on upper scopes.
8 "reap", "localize", "localize_elem", "localize_delete" and "WORDS" :
13 reap localize localize_elem localize_delete
18 my ($class, $name) = @_;
20 localize '$tag' => bless({ name => $name }, $class) => UP;
22 reap { print Scope->tag->name, ": end\n" } UP;
25 # Get the tag stored in the caller namespace
28 my $pkg = __PACKAGE__;
29 $pkg = caller $l++ while $pkg eq __PACKAGE__;
35 sub name { shift->{name} }
37 # Locally capture warnings and reprint them with the name prefixed
39 localize_elem '%SIG', '__WARN__' => sub {
40 print Scope->tag->name, ': ', @_;
46 for (reverse 0 .. $#INC) {
47 # First UP is the for loop, second is the sub boundary
48 localize_delete '@INC', $_ => UP UP;
57 Scope->new("top"); # initializes $UserLand::tag
61 my $one = 1 + undef; # prints "top: Use of uninitialized value..."
66 print $@; # prints "Can't locate Cwd.pm in @INC
67 } # (@INC contains:) at..."
69 require Cwd; # loads Cwd.pm
72 } # prints "top: done"
74 "unwind" and "want_at" :
78 use Scope::Upper qw<unwind want_at :words>;
81 my @result = shift->();
82 my $cx = SUB UP; # Point to the sub above this one
83 unwind +(want_at($cx) ? @result : scalar @result) => $cx;
90 my @things = qw<a b c>;
91 return @things; # returns to try() and then outside zap()
97 my @stuff = zap(); # @stuff contains qw<a b c>
98 my $stuff = zap(); # $stuff contains 3
104 use Scope::Upper qw<uplevel CALLER>;
112 my $sub = (caller 0)[3];
113 print "$_[0] from $sub()";
117 target('hello'); # "hello from Uplevel::target()"
119 "uid" and "validate_uid" :
121 use Scope::Upper qw<uid validate_uid>;
128 if ($uid eq uid(UP)) { # yes
131 if (validate_uid($uid)) { # yes
137 if (validate_uid($uid)) { # no
142 This module lets you defer actions *at run-time* that will take place
143 when the control flow returns into an upper scope. Currently, you can:
145 * hook an upper scope end with "reap" ;
147 * localize variables, array/hash values or deletions of elements in
148 higher contexts with respectively "localize", "localize_elem" and
151 * return values immediately to an upper level with "unwind", "yield"
154 * gather information about an upper context with "want_at" and
157 * execute a subroutine in the setting of an upper subroutine stack
158 frame with "uplevel" ;
160 * uniquely identify contexts with "uid" and "validate_uid".
163 In all those functions, $context refers to the target scope.
165 You have to use one or a combination of "WORDS" to build the $context
166 passed to these functions. This is needed in order to ensure that the
167 module still works when your program is ran in the debugger. The only
168 thing you can assume is that it is an *absolute* indicator of the frame,
169 which means that you can safely store it at some point and use it when
170 needed, and it will still denote the original scope.
174 reap { ... } $context;
175 &reap($callback, $context);
177 Adds a destructor that calls $callback (in void context) when the upper
178 scope represented by $context ends.
181 localize $what, $value;
182 localize $what, $value, $context;
184 Introduces a "local" delayed to the time of first return into the upper
185 scope denoted by $context. $what can be :
187 * A glob, in which case $value can either be a glob or a reference.
188 "localize" follows then the same syntax as "local *x = $value". For
189 example, if $value is a scalar reference, then the "SCALAR" slot of
190 the glob will be set to $$value - just like "local *x = \1" sets $x
193 * A string beginning with a sigil, representing the symbol to localize
194 and to assign to. If the sigil is '$', "localize" follows the same
195 syntax as "local $x = $value", i.e. $value isn't dereferenced. For
198 localize '$x', \'foo' => HERE;
200 will set $x to a reference to the string 'foo'. Other sigils ('@',
201 '%', '&' and '*') require $value to be a reference of the
204 When the symbol is given by a string, it is resolved when the actual
205 localization takes place and not when "localize" is called. Thus, if
206 the symbol name is not qualified, it will refer to the variable in
207 the package where the localization actually takes place and not in
208 the one where the "localize" call was compiled. For example,
212 sub new { localize '$tag', $_[0] => UP }
223 will localize $Tool::tag and not $Scope::tag. If you want the other
224 behaviour, you just have to specify $what as a glob or a qualified
227 Note that if $what is a string denoting a variable that wasn't
228 declared beforehand, the relevant slot will be vivified as needed
229 and won't be deleted from the glob when the localization ends. This
230 situation never arises with "local" because it only compiles when
231 the localized variable is already declared. Although I believe it
232 shouldn't be a problem as glob slots definedness is pretty much an
233 implementation detail, this behaviour may change in the future if
237 localize_elem $what, $key, $value;
238 localize_elem $what, $key, $value, $context;
240 Introduces a "local $what[$key] = $value" or "local $what{$key} =
241 $value" delayed to the time of first return into the upper scope denoted
242 by $context. Unlike "localize", $what must be a string and the type of
243 localization is inferred from its sigil. The two only valid types are
244 array and hash ; for anything besides those, "localize_elem" will throw
245 an exception. $key is either an array index or a hash key, depending of
246 which kind of variable you localize.
248 If $what is a string pointing to an undeclared variable, the variable
249 will be vivified as soon as the localization occurs and emptied when it
250 ends, although it will still exist in its glob.
253 localize_delete $what, $key;
254 localize_delete $what, $key, $context;
256 Introduces the deletion of a variable or an array/hash element delayed
257 to the time of first return into the upper scope denoted by $context.
260 * A glob, in which case $key is ignored and the call is equivalent to
263 * A string beginning with '@' or '%', for which the call is equivalent
264 to respectively "local $a[$key]; delete $a[$key]" and "local
265 $h{$key}; delete $h{$key}".
267 * A string beginning with '&', which more or less does "undef &func"
268 in the upper scope. It's actually more powerful, as &func won't even
269 "exists" anymore. $key is ignored.
273 unwind @values, $context;
275 Returns @values *from* the subroutine, eval or format context pointed by
276 or just above $context, and immediately restarts the program flow at
277 this point - thus effectively returning @values to an upper scope. If
278 @values is empty, then the $context parameter is optional and defaults
279 to the current context (making the call equivalent to a bare "return;")
280 ; otherwise it is mandatory.
282 The upper context isn't coerced onto @values, which is hence always
283 evaluated in list context. This means that
286 my @a = ('a' .. 'z');
291 will set $num to 'z'. You can use "want_at" to handle these cases.
295 yield @values, $context;
297 Returns @values *from* the context pointed by or just above $context,
298 and immediately restarts the program flow at this point. If @values is
299 empty, then the $context parameter is optional and defaults to the
300 current context ; otherwise it is mandatory.
302 "yield" differs from "unwind" in that it can target *any* upper scope
303 (besides a "s///e" substitution context) and not necessarily a sub, an
304 eval or a format. Hence you can use it to return values from a "do" or a
309 eval { require Time::HiRes } or yield time() => HERE;
314 yield if $seen{$_}++; # returns the empty list from the block
318 Like for "unwind", the upper context isn't coerced onto @values. You can
319 use the fifth value returned by "context_info" to handle context
326 Immediately returns @values from the current block, whatever it may be
327 (besides a "s///e" substitution context). "leave" is actually a synonym
328 for "yield HERE", while "leave @values" is a synonym for "yield @values,
331 Like for "yield", you can use the fifth value returned by "context_info"
332 to handle context coercion.
336 my $want = want_at $context;
338 Like "wantarray" in perlfunc, but for the subroutine, eval or format
339 context located at or just above $context.
341 It can be used to revise the example showed in "unwind" :
344 my @a = ('a' .. 'z');
345 unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
349 will rightfully set $num to 26.
352 my ($package, $filename, $line, $subroutine, $hasargs,
353 $wantarray, $evaltext, $is_require, $hints, $bitmask,
354 $hinthash) = context_info $context;
356 Gives information about the context denoted by $context, akin to what
357 "caller" in perlfunc provides but not limited only to subroutine, eval
358 and format contexts. When $context is omitted, it defaults to the
361 The returned values are, in order :
363 * *(index 0)* : the namespace in use when the context was created ;
365 * *(index 1)* : the name of the file at the point where the context
368 * *(index 2)* : the line number at the point where the context was
371 * *(index 3)* : the name of the subroutine called for this context, or
372 "undef" if this is not a subroutine context ;
374 * *(index 4)* : a boolean indicating whether a new instance of @_ was
375 set up for this context, or "undef" if this is not a subroutine
378 * *(index 5)* : the context (in the sense of "wantarray" in perlfunc)
379 in which the context (in our sense) is executed ;
381 * *(index 6)* : the contents of the string being compiled for this
382 context, or "undef" if this is not an eval context ;
384 * *(index 7)* : a boolean indicating whether this eval context was
385 created by "require", or "undef" if this is not an eval context ;
387 * *(index 8)* : the value of the lexical hints in use when the context
390 * *(index 9)* : a bit string representing the warnings in use when the
391 context was created ;
393 * *(index 10)* : a reference to the lexical hints hash in use when the
394 context was created (only on perl 5.10 or greater).
397 my @ret = uplevel { ...; return @ret };
398 my @ret = uplevel { my @args = @_; ...; return @ret } @args, $context;
399 my @ret = &uplevel($callback, @args, $context);
401 Executes the code reference $callback with arguments @args as if it were
402 located at the subroutine stack frame pointed by $context, effectively
403 fooling "caller" and "die" into believing that the call actually
404 happened higher in the stack. The code is executed in the context of the
405 "uplevel" call, and what it returns is returned as-is by "uplevel".
417 my @inverses = target(1, 2, 4); # @inverses contains (0, 0.5, 0.25)
418 my $count = target(1, 2, 4); # $count is 3
420 Note that if @args is empty, then the $context parameter is optional and
421 defaults to the current context ; otherwise it is mandatory.
423 Sub::Uplevel also implements a pure-Perl version of "uplevel". Both are
424 identical, with the following caveats :
426 * The Sub::Uplevel implementation of "uplevel" may execute a code
427 reference in the context of any upper stack frame. The Scope::Upper
428 version can only uplevel to a subroutine stack frame, and will croak
429 if you try to target an "eval" or a format.
431 * Exceptions thrown from the code called by this version of "uplevel"
432 will not be caught by "eval" blocks between the target frame and the
433 uplevel call, while they will for Sub::Uplevel's version. This means
441 uplevel { die 'wut' } CALLER(2); # for Scope::Upper
442 # uplevel(3, sub { die 'wut' }) # for Sub::Uplevel
445 print "inner block: $@";
449 print "outer block: $@";
451 will print "inner block: wut..." with Sub::Uplevel and "outer block:
452 wut..." with Scope::Upper.
454 * Sub::Uplevel globally overrides the Perl keyword "caller", while
455 Scope::Upper does not.
457 A simple wrapper lets you mimic the interface of "uplevel" in
465 my $cxt = Scope::Upper::CALLER($frame);
466 &Scope::Upper::uplevel($code => @_ => $cxt);
469 Albeit the three exceptions listed above, it passes all the tests of
474 my $uid = uid $context;
476 Returns an unique identifier (UID) for the context (or dynamic scope)
477 pointed by $context, or for the current context if $context is omitted.
478 This UID will only be valid for the life time of the context it
479 represents, and another UID will be generated next time the same scope
486 if ($uid eq uid()) { # yes, this is the same context
490 if ($uid eq uid()) { # no, we are one scope below
493 if ($uid eq uid(UP)) { # yes, UP points to the same scope as $uid
499 # $uid is now invalid
502 if ($uid eq uid()) { # no, this is another block
507 For example, each loop iteration gets its own UID :
516 # %uids has 5 entries
518 The UIDs are not guaranteed to be numbers, so you must use the "eq"
519 operator to compare them.
521 To check whether a given UID is valid, you can use the "validate_uid"
525 my $is_valid = validate_uid $uid;
527 Returns true if and only if $uid is the UID of a currently valid context
528 (that is, it designates a scope that is higher than the current one in
535 if (validate_uid($uid)) { # yes
539 if (validate_uid($uid)) { # yes
545 if (validate_uid($uid)) { # no
551 True iff the module could have been built when thread-safety features.
556 my $top_context = TOP;
558 Returns the context that currently represents the highest scope.
561 my $current_context = HERE;
563 The context of the current scope.
565 Getting a context from a context
566 For any of those functions, $from is expected to be a context. When
567 omitted, it defaults to the current context.
570 my $upper_context = UP;
571 my $upper_context = UP $from;
573 The context of the scope just above $from.
576 my $sub_context = SUB;
577 my $sub_context = SUB $from;
579 The context of the closest subroutine above $from. Note that $from is
580 returned if it is already a subroutine context ; hence "SUB SUB == SUB".
583 my $eval_context = EVAL;
584 my $eval_context = EVAL $from;
586 The context of the closest eval above $from. Note that $from is returned
587 if it is already an eval context ; hence "EVAL EVAL == EVAL".
589 Getting a context from a level
590 Here, $level should denote a number of scopes above the current one.
591 When omitted, it defaults to 0 and those functions return the same
596 my $context = SCOPE $level;
598 The $level-th upper context, regardless of its type.
601 my $context = CALLER;
602 my $context = CALLER $level;
604 The context of the $level-th upper subroutine/eval/format. It kind of
605 corresponds to the context represented by "caller $level", but while
606 e.g. "caller 0" refers to the caller context, "CALLER 0" will refer to
607 the top scope in the current context.
610 Where "reap" fires depending on the $cxt :
616 reap \&cleanup => $cxt;
618 } # $cxt = SCOPE(0) = HERE
620 }->(); # $cxt = SCOPE(1) = UP = SUB = CALLER(0)
622 }; # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1)
624 }->(); # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2)
627 Where "localize", "localize_elem" and "localize_delete" act depending on
634 localize '$x' => 1 => $cxt;
635 # $cxt = SCOPE(0) = HERE
638 # $cxt = SCOPE(1) = UP = SUB = CALLER(0)
641 # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1)
644 # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2)
647 # $cxt = SCOPE(4), UP SUB UP SUB = UP SUB EVAL = UP CALLER(2) = TOP
650 Where "unwind", "yield", "want_at", "context_info" and "uplevel" point
651 to depending on the $cxt:
657 unwind @things => $cxt; # or yield @things => $cxt
658 # or uplevel { ... } $cxt
662 }->(); # $cxt = SCOPE(0) = SCOPE(1) = HERE = UP = SUB = CALLER(0)
664 }; # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1) (*)
666 }->(); # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2)
669 # (*) Note that uplevel() will croak if you pass that scope frame,
670 # because it cannot target eval scopes.
673 The functions "reap", "localize", "localize_elem", "localize_delete",
674 "unwind", "yield", "leave", "want_at", "context_info" and "uplevel" are
675 only exported on request, either individually or by the tags ':funcs'
678 The constant "SU_THREADSAFE" is also only exported on request,
679 individually or by the tags ':consts' and ':all'.
681 Same goes for the words "TOP", "HERE", "UP", "SUB", "EVAL", "SCOPE" and
682 "CALLER" that are only exported on request, individually or by the tags
686 Be careful that local variables are restored in the reverse order in
687 which they were localized. Consider those examples:
691 reap sub { print $x } => HERE;
699 reap sub { $x = 2 } => HERE;
704 The first case is "solved" by moving the "local" before the "reap", and
705 the second by using "localize" instead of "reap".
707 The effects of "reap", "localize" and "localize_elem" can't cross
708 "BEGIN" blocks, hence calling those functions in "import" is deemed to
709 be useless. This is an hopeless case because "BEGIN" blocks are executed
710 once while localizing constructs should do their job at each run.
711 However, it's possible to hook the end of the current scope compilation
712 with B::Hooks::EndOfScope.
714 Some rare oddities may still happen when running inside the debugger. It
715 may help to use a perl higher than 5.8.9 or 5.10.0, as they contain some
716 context-related fixes.
718 Calling "goto" to replace an "uplevel"'d code frame does not work :
720 * for a "perl" older than the 5.8 series ;
722 * for a "DEBUGGING" "perl" run with debugging flags set (as in "perl
725 * when the runloop callback is replaced by another module.
727 In those three cases, "uplevel" will look for a "goto &sub" statement in
728 its callback and, if there is one, throw an exception before executing
731 Moreover, in order to handle "goto" statements properly, "uplevel"
732 currently has to suffer a run-time overhead proportional to the size of
733 the callback in every case (with a small ratio), and proportional to the
734 size of all the code executed as the result of the "uplevel" call
735 (including subroutine calls inside the callback) when a "goto" statement
736 is found in the "uplevel" callback. Despite this shortcoming, this XS
737 version of "uplevel" should still run way faster than the pure-Perl
738 version from Sub::Uplevel.
743 A C compiler. This module may happen to build with a C++ compiler as
744 well, but don't rely on it, as no guarantee is made in this regard.
746 XSLoader (core since perl 5.6.0).
749 "local" in perlfunc, "Temporary Values via local()" in perlsub.
751 Alias, Hook::Scope, Scope::Guard, Guard.
755 Continuation::Escape is a thin wrapper around Scope::Upper that gives
756 you a continuation passing style interface to "unwind". It's easier to
757 use, but it requires you to have control over the scope where you want
763 Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
765 You can contact me by mail or on "irc.perl.org" (vincent).
768 Please report any bugs or feature requests to "bug-scope-upper at
769 rt.cpan.org", or through the web interface at
770 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Scope-Upper>. I will be
771 notified, and then you'll automatically be notified of progress on your
772 bug as I make changes.
775 You can find documentation for this module with the perldoc command.
779 Tests code coverage report is available at
780 <http://www.profvince.com/perl/cover/Scope-Upper>.
783 Inspired by Ricardo Signes.
785 Thanks to Shawn M. Moore for motivation.
788 Copyright 2008,2009,2010,2011,2012,2013 Vincent Pit, all rights
791 This program is free software; you can redistribute it and/or modify it
792 under the same terms as Perl itself.