X-Git-Url: http://git.vpit.fr/?a=blobdiff_plain;f=README;h=7d441b7558fa36830cac4af0e6297130b6b95c27;hb=70187dc24bb0f90a81f58ff2bd52ba7d9c3ac06f;hp=8dd7b5d74759860924adbc5b5fa70414af196113;hpb=cf46c3456f20acba34dd6543ea76de3b84b47401;p=perl%2Fmodules%2FScope-Upper.git diff --git a/README b/README index 8dd7b5d..7d441b7 100644 --- a/README +++ b/README @@ -2,53 +2,84 @@ NAME Scope::Upper - Act on upper scopes. VERSION - Version 0.06 + Version 0.18 SYNOPSIS - package X; + "reap", "localize", "localize_elem", "localize_delete" and "WORDS" : - use Scope::Upper qw/reap localize localize_elem localize_delete :words/; + package Scope; - sub desc { shift->{desc} } + use Scope::Upper qw< + reap localize localize_elem localize_delete + :words + >; - sub set_tag { - my ($desc) = @_; + sub new { + my ($class, $name) = @_; - # First localize $x so that it gets destroyed last - localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP; # one scope up + localize '$tag' => bless({ name => $name }, $class) => UP; - reap sub { - my $pkg = caller; - my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope - print $x->desc . ": done\n"; - } => SCOPE 1; # same as UP here + reap { print Scope->tag->name, ": end\n" } UP; + } + + # Get the tag stored in the caller namespace + sub tag { + my $l = 0; + my $pkg = __PACKAGE__; + $pkg = caller $l++ while $pkg eq __PACKAGE__; + + no strict 'refs'; + ${$pkg . '::tag'}; + } + sub name { shift->{name} } + + # Locally capture warnings and reprint them with the name prefixed + sub catch { localize_elem '%SIG', '__WARN__' => sub { - my $pkg = caller; - my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope - CORE::warn($x->desc . ': ' . join('', @_)); - } => UP CALLER 0; # same as UP here + print Scope->tag->name, ': ', @_; + } => UP; + } - # delete last @ARGV element - localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here + # Locally clear @INC + sub private { + for (reverse 0 .. $#INC) { + # First UP is the for loop, second is the sub boundary + localize_delete '@INC', $_ => UP UP; + } } - package Y; + ... + + package UserLand; { - X::set_tag('pie'); - # $x is now a X object, and @ARGV has one element less - warn 'what'; # warns "pie: what at ..." - ... - } # "pie: done" is printed + Scope->new("top"); # initializes $UserLand::tag + + { + Scope->catch; + my $one = 1 + undef; # prints "top: Use of uninitialized value..." + + { + Scope->private; + eval { require Cwd }; + print $@; # prints "Can't locate Cwd.pm in @INC + } # (@INC contains:) at..." + + require Cwd; # loads Cwd.pm + } + + } # prints "top: done" - package Z; + "unwind" and "want_at" : - use Scope::Upper qw/unwind want_at :words/; + package Try; + + use Scope::Upper qw; sub try (&) { my @result = shift->(); - my $cx = SUB UP SUB; + my $cx = SUB UP; # Point to the sub above this one unwind +(want_at($cx) ? @result : scalar @result) => $cx; } @@ -56,38 +87,92 @@ SYNOPSIS sub zap { try { + my @things = qw; return @things; # returns to try() and then outside zap() + # not reached + }; + # not reached + } + + my @stuff = zap(); # @stuff contains qw + my $stuff = zap(); # $stuff contains 3 + + "uplevel" : + + package Uplevel; + + use Scope::Upper qw; + + sub target { + faker(@_); + } + + sub faker { + uplevel { + my $sub = (caller 0)[3]; + print "$_[0] from $sub()"; + } @_ => CALLER(1); + } + + target('hello'); # "hello from Uplevel::target()" + + "uid" and "validate_uid" : + + use Scope::Upper qw; + + my $uid; + + { + $uid = uid(); + { + if ($uid eq uid(UP)) { # yes + ... + } + if (validate_uid($uid)) { # yes + ... + } } } - my @what = zap(); # @what contains @things + if (validate_uid($uid)) { # no + ... + } DESCRIPTION - This module lets you defer actions that will take place when the control - flow returns into an upper scope. Currently, you can hook an upper scope - end, or localize variables, array/hash values or deletions of elements - in higher contexts. You can also return to an upper level and know which - context was in use then. + This module lets you defer actions *at run-time* that will take place + when the control flow returns into an upper scope. Currently, you can: + + * hook an upper scope end with "reap" ; + + * localize variables, array/hash values or deletions of elements in + higher contexts with respectively "localize", "localize_elem" and + "localize_delete" ; + + * return values immediately to an upper level with "unwind", and know + which context was in use then with "want_at" ; + + * execute a subroutine in the setting of an upper subroutine stack + frame with "uplevel" ; + + * uniquely identify contextes with "uid" and "validate_uid". FUNCTIONS In all those functions, $context refers to the target scope. - You have to use one or a combination of "WORDS" to build the $context to - pass to these functions. This is needed in order to ensure that the - module still works when your program is ran in the debugger. Don't try - to use a raw value or things will get messy. - - The only thing you can assume is that it is an *absolute* indicator of - the frame. This means that you can safely store it at some point and use - it when needed, and it will still denote the original scope. + You have to use one or a combination of "WORDS" to build the $context + passed to these functions. This is needed in order to ensure that the + module still works when your program is ran in the debugger. The only + thing you can assume is that it is an *absolute* indicator of the frame, + which means that you can safely store it at some point and use it when + needed, and it will still denote the original scope. "reap $callback, $context" - Add a destructor that calls $callback when the upper scope represented - by $context ends. + Adds a destructor that calls $callback (in void context) when the upper + scope represented by $context ends. "localize $what, $value, $context" - A "local" delayed to the time of first return into the upper scope - denoted by $context. $what can be : + Introduces a "local" delayed to the time of first return into the upper + scope denoted by $context. $what can be : * A glob, in which case $value can either be a glob or a reference. "localize" follows then the same syntax as "local *x = $value". For @@ -107,22 +192,54 @@ FUNCTIONS corresponding type. When the symbol is given by a string, it is resolved when the actual - localization takes place and not when "localize" is called. This - means that - - sub tag { localize '$x', $_[0] => UP } - - will localize in the caller's namespace. + localization takes place and not when "localize" is called. Thus, if + the symbol name is not qualified, it will refer to the variable in + the package where the localization actually takes place and not in + the one where the "localize" call was compiled. For example, + + { + package Scope; + sub new { localize '$tag', $_[0] => UP } + } + + { + package Tool; + { + Scope->new; + ... + } + } + + will localize $Tool::tag and not $Scope::tag. If you want the other + behaviour, you just have to specify $what as a glob or a qualified + name. + + Note that if $what is a string denoting a variable that wasn't + declared beforehand, the relevant slot will be vivified as needed + and won't be deleted from the glob when the localization ends. This + situation never arises with "local" because it only compiles when + the localized variable is already declared. Although I believe it + shouldn't be a problem as glob slots definedness is pretty much an + implementation detail, this behaviour may change in the future if + proved harmful. "localize_elem $what, $key, $value, $context" - Similar to "localize" but for array and hash elements. If $what is a - glob, the slot to fill is determined from which type of reference $value - is ; otherwise it's inferred from the sigil. $key is either an array - index or a hash key, depending of which kind of variable you localize. + Introduces a "local $what[$key] = $value" or "local $what{$key} = + $value" delayed to the time of first return into the upper scope denoted + by $context. Unlike "localize", $what must be a string and the type of + localization is inferred from its sigil. The two only valid types are + array and hash ; for anything besides those, "localize_elem" will throw + an exception. $key is either an array index or a hash key, depending of + which kind of variable you localize. + + If $what is a string pointing to an undeclared variable, the variable + will be vivified as soon as the localization occurs and emptied when it + ends, although it will still exist in its glob. "localize_delete $what, $key, $context" - Similiar to "localize", but for deleting variables or array/hash - elements. $what can be: + Introduces the deletion of a variable or an array/hash element delayed + to the time of first return into the upper scope denoted by $context. + $what can be: * A glob, in which case $key is ignored and the call is equivalent to "local *x". @@ -137,7 +254,9 @@ FUNCTIONS "unwind @values, $context" Returns @values *from* the context pointed by $context, i.e. from the - subroutine, eval or format just above $context. + subroutine, eval or format at or just above $context, and immediately + restart the program flow at this point - thus effectively returning to + an upper scope. The upper context isn't coerced onto @values, which is hence always evaluated in list context. This means that @@ -145,12 +264,13 @@ FUNCTIONS my $num = sub { my @a = ('a' .. 'z'); unwind @a => HERE; + # not reached }->(); will set $num to 'z'. You can use "want_at" to handle these cases. "want_at $context" - Like "wantarray", but for the subroutine/eval/format just above + Like "wantarray", but for the subroutine/eval/format at or just above $context. The previous example can then be "corrected" : @@ -158,9 +278,155 @@ FUNCTIONS my $num = sub { my @a = ('a' .. 'z'); unwind +(want_at(HERE) ? @a : scalar @a) => HERE; + # not reached }->(); - will righteously set $num to 26. + will rightfully set $num to 26. + + "uplevel $code, @args, $context" + Executes the code reference $code with arguments @args as if it were + located at the subroutine stack frame pointed by $context, effectively + fooling "caller" and "die" into believing that the call actually + happened higher in the stack. The code is executed in the context of the + "uplevel" call, and what it returns is returned as-is by "uplevel". + + sub target { + faker(@_); + } + + sub faker { + uplevel { + map { 1 / $_ } @_; + } @_ => CALLER(1); + } + + my @inverses = target(1, 2, 4); # @inverses contains (0, 0.5, 0.25) + my $count = target(1, 2, 4); # $count is 3 + + Sub::Uplevel also implements a pure-Perl version of "uplevel". Both are + identical, with the following caveats : + + * The Sub::Uplevel implementation of "uplevel" may execute a code + reference in the context of any upper stack frame. The Scope::Upper + version can only uplevel to a subroutine stack frame, and will croak + if you try to target an "eval" or a format. + + * Exceptions thrown from the code called by this version of "uplevel" + will not be caught by "eval" blocks between the target frame and the + uplevel call, while they will for Sub::Uplevel's version. This means + that : + + eval { + sub { + local $@; + eval { + sub { + uplevel { die 'wut' } CALLER(2); # for Scope::Upper + # uplevel(3, sub { die 'wut' }) # for Sub::Uplevel + }->(); + }; + print "inner block: $@"; + $@ and exit; + }->(); + }; + print "outer block: $@"; + + will print "inner block: wut..." with Sub::Uplevel and "outer block: + wut..." with Scope::Upper. + + * Sub::Uplevel globally overrides the Perl keyword "caller", while + Scope::Upper does not. + + A simple wrapper lets you mimic the interface of "uplevel" in + Sub::Uplevel : + + use Scope::Upper; + + sub uplevel { + my $frame = shift; + my $code = shift; + my $cxt = Scope::Upper::CALLER($frame); + &Scope::Upper::uplevel($code => @_ => $cxt); + } + + Albeit the three exceptions listed above, it passes all the tests of + Sub::Uplevel. + + "uid $context" + Returns an unique identifier (UID) for the context (or dynamic scope) + pointed by $context, or for the current context if $context is omitted. + This UID will only be valid for the life time of the context it + represents, and another UID will be generated next time the same scope + is executed. + + my $uid; + + { + $uid = uid; + if ($uid eq uid()) { # yes, this is the same context + ... + } + { + if ($uid eq uid()) { # no, we are one scope below + ... + } + if ($uid eq uid(UP)) { # yes, UP points to the same scope as $uid + ... + } + } + } + + # $uid is now invalid + + { + if ($uid eq uid()) { # no, this is another block + ... + } + } + + For example, each loop iteration gets its own UID : + + my %uids; + + for (1 .. 5) { + my $uid = uid; + $uids{$uid} = $_; + } + + # %uids has 5 entries + + The UIDs are not guaranteed to be numbers, so you must use the "eq" + operator to compare them. + + To check whether a given UID is valid, you can use the "validate_uid" + function. + + "validate_uid $uid" + Returns true if and only if $uid is the UID of a currently valid context + (that is, it designates a scope that is higher than the current one in + the call stack). + + my $uid; + + { + $uid = uid(); + if (validate_uid($uid)) { # yes + ... + } + { + if (validate_uid($uid)) { # yes + ... + } + } + } + + if (validate_uid($uid)) { # no + ... + } + +CONSTANTS + "SU_THREADSAFE" + True iff the module could have been built when thread-safety features. WORDS Constants @@ -178,10 +444,12 @@ WORDS The context of the scope just above $from. "SUB $from" - The context of the closest subroutine above $from. + The context of the closest subroutine above $from. Note that $from is + returned if it is already a subroutine context ; hence "SUB SUB == SUB". "EVAL $from" - The context of the closest eval above $from. + The context of the closest eval above $from. Note that $from is returned + if it is already an eval context ; hence "EVAL EVAL == EVAL". Getting a context from a level Here, $level should denote a number of scopes above the current one. @@ -197,10 +465,74 @@ WORDS e.g. "caller 0" refers to the caller context, "CALLER 0" will refer to the top scope in the current context. + Examples + Where "reap" fires depending on the $cxt : + + sub { + eval { + sub { + { + reap \&cleanup => $cxt; + ... + } # $cxt = SCOPE(0) = HERE + ... + }->(); # $cxt = SCOPE(1) = UP = SUB = CALLER(0) + ... + }; # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1) + ... + }->(); # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2) + ... + + Where "localize", "localize_elem" and "localize_delete" act depending on + the $cxt : + + sub { + eval { + sub { + { + localize '$x' => 1 => $cxt; + # $cxt = SCOPE(0) = HERE + ... + } + # $cxt = SCOPE(1) = UP = SUB = CALLER(0) + ... + }->(); + # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1) + ... + }; + # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2) + ... + }->(); + # $cxt = SCOPE(4), UP SUB UP SUB = UP SUB EVAL = UP CALLER(2) = TOP + ... + + Where "unwind", "want_at" and "uplevel" point to depending on the $cxt: + + sub { + eval { + sub { + { + unwind @things => $cxt; # or uplevel { ... } $cxt; + ... + } + ... + }->(); # $cxt = SCOPE(0) = SCOPE(1) = HERE = UP = SUB = CALLER(0) + ... + }; # $cxt = SCOPE(2) = UP UP = UP SUB = EVAL = CALLER(1) (*) + ... + }->(); # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2) + ... + + # (*) Note that uplevel() will croak if you pass that scope frame, + # because it cannot target eval scopes. + EXPORT The functions "reap", "localize", "localize_elem", "localize_delete", - "unwind" and "want_at" are only exported on request, either individually - or by the tags ':funcs' and ':all'. + "unwind", "want_at" and "uplevel" are only exported on request, either + individually or by the tags ':funcs' and ':all'. + + The constant "SU_THREADSAFE" is also only exported on request, + individually or by the tags ':consts' and ':all'. Same goes for the words "TOP", "HERE", "UP", "SUB", "EVAL", "SCOPE" and "CALLER" that are only exported on request, individually or by the tags @@ -228,21 +560,56 @@ CAVEATS The first case is "solved" by moving the "local" before the "reap", and the second by using "localize" instead of "reap". - "reap", "localize" and "localize_elem" effects can't cross "BEGIN" - blocks, hence calling those functions in "import" is deemed to be - useless. This is an hopeless case because "BEGIN" blocks are executed + The effects of "reap", "localize" and "localize_elem" can't cross + "BEGIN" blocks, hence calling those functions in "import" is deemed to + be useless. This is an hopeless case because "BEGIN" blocks are executed once while localizing constructs should do their job at each run. + However, it's possible to hook the end of the current scope compilation + with B::Hooks::EndOfScope. Some rare oddities may still happen when running inside the debugger. It may help to use a perl higher than 5.8.9 or 5.10.0, as they contain some - context fixes. + context-related fixes. + + Calling "goto" to replace an "uplevel"'d code frame does not work : + + * for a "perl" older than the 5.8 series ; + + * for a "DEBUGGING" "perl" run with debugging flags set (as in "perl + -D ...") ; + + * when the runloop callback is replaced by another module. + + In those three cases, "uplevel" will look for a "goto &sub" statement in + its callback and, if there is one, throw an exception before executing + the code. + + Moreover, in order to handle "goto" statements properly, "uplevel" + currently has to suffer a run-time overhead proportional to the size of + the the callback in every case (with a small ratio), and proportional to + the size of all the code executed as the result of the "uplevel" call + (including subroutine calls inside the callback) when a "goto" statement + is found in the "uplevel" callback. Despite this shortcoming, this XS + version of "uplevel" should still run way faster than the pure-Perl + version from Sub::Uplevel. DEPENDENCIES XSLoader (standard since perl 5.006). SEE ALSO + "local" in perlfunc, "Temporary Values via local()" in perlsub. + Alias, Hook::Scope, Scope::Guard, Guard. + Sub::Uplevel. + + Continuation::Escape is a thin wrapper around Scope::Upper that gives + you a continuation passing style interface to "unwind". It's easier to + use, but it requires you to have control over the scope where you want + to return. + + Scope::Escape. + AUTHOR Vincent Pit, "", . @@ -269,7 +636,7 @@ ACKNOWLEDGEMENTS Thanks to Shawn M. Moore for motivation. COPYRIGHT & LICENSE - Copyright 2008-2009 Vincent Pit, all rights reserved. + Copyright 2008,2009,2010,2011 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.