X-Git-Url: http://git.vpit.fr/?a=blobdiff_plain;f=README;h=7b6405aea649135bfa3912d58687dc3bf3e3fb38;hb=d965a45a64e2aab24e3adbda18543e80a0b81e57;hp=52a76112f566173d0ffce5d8df265a5df69b955c;hpb=bac4fc46c2d48ce5db75de6c88e0983aeeedf865;p=perl%2Fmodules%2FScope-Upper.git diff --git a/README b/README index 52a7611..7b6405a 100644 --- a/README +++ b/README @@ -2,56 +2,128 @@ NAME Scope::Upper - Act on upper scopes. VERSION - Version 0.01 + Version 0.13 SYNOPSIS - package X; + "reap", "localize", "localize_elem", "localize_delete" and "WORDS" : - use Scope::Upper qw/reap localize localize_elem/; + 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 => $desc }, __PACKAGE__) => 1; + localize '$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"; - } => 1; + 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('', @_)); - } => 1; + print Scope->tag->name, ': ', @_; + } => UP; } - package Y; + # 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 UserLand; { - X::set_tag('pie'); - # $x is now a X object - 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" + + "unwind" and "want_at" : + + package Try; + + use Scope::Upper qw/unwind want_at :words/; + + sub try (&) { + my @result = shift->(); + my $cx = SUB UP; # Point to the sub above this one + unwind +(want_at($cx) ? @result : scalar @result) => $cx; + } + + ... + + sub zap { + try { + my @things = qw/a b c/; + return @things; # returns to try() and then outside zap() + # not reached + }; + # not reached + } + + my @stuff = zap(); # @stuff contains qw/a b c/ + my $stuff = zap(); # $stuff contains 3 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 and array/hash values in higher contexts. + 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". FUNCTIONS - "reap $callback, $level" - Add a destructor that calls $callback when the $level-th upper scope - ends, where 0 corresponds to the current scope. + In all those functions, $context refers to the target scope. - "localize $what, $value, $level" - A "local" delayed to the time of first return into the $level-th upper - scope. $what can be : + 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" + Adds a destructor that calls $callback (in void context) when the upper + scope represented by $context ends. + + "localize $what, $value, $context" + 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 = $value". For @@ -60,41 +132,267 @@ FUNCTIONS to 1. * A string beginning with a sigil, representing the symbol to localize - and assign to. If the sigil is '$', then $value isn't dereferenced, - that is + and to assign to. If the sigil is '$', "localize" follows the same + syntax as "local $x = $value", i.e. $value isn't dereferenced. For + example, + + localize '$x', \'foo' => HERE; + + will set $x to a reference to the string 'foo'. Other sigils ('@', + '%', '&' and '*') require $value to be a reference of the + corresponding type. + + When the symbol is given by a string, it is resolved when the actual + localization takes place and not when "localize" is called. Thus, if + the symbol name is not qualified, it will refer to the variable in + the package where the localization actually takes place and not in + the one where the "localize" call was compiled. For example, + + { + package Scope; + sub new { localize '$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" + 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" + 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". + + * A string beginning with '@' or '%', for which the call is equivalent + to respectiveley "local $a[$key]; delete $a[$key]" and "local + $h{$key}; delete $h{$key}". + + * A string beginning with '&', which more or less does "undef &func" + in the upper scope. It's actually more powerful, as &func won't even + "exists" anymore. $key is ignored. + + "unwind @values, $context" + Returns @values *from* the context pointed by $context, i.e. from the + 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 + + 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 at or just above + $context. + + The previous example can then be "corrected" : + + my $num = sub { + my @a = ('a' .. 'z'); + unwind +(want_at(HERE) ? @a : scalar @a) => HERE; + # not reached + }->(); + + will rightfully set $num to 26. + +CONSTANTS + "SU_THREADSAFE" + True iff the module could have been built when thread-safety features. + +WORDS + Constants + "TOP" + Returns the context that currently represents the highest scope. + + "HERE" + The context of the current scope. + + Getting a context from a context + For any of those functions, $from is expected to be a context. When + omitted, it defaults to the the current context. + + "UP $from" + The context of the scope just above $from. + + "SUB $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. 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. + When omitted, it defaults to 0 and those functions return the same + context as "HERE". + + "SCOPE $level" + The $level-th upper context, regardless of its type. + + "CALLER $level" + The context of the $level-th upper subroutine/eval/format. It kind of + corresponds to the context represented by "caller $level", but while + 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), or HERE + ... + }->(); # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0) + ... + }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) + ... + }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) + ... + + Where "localize", "localize_elem" and "localize_delete" act depending on + the $cxt : + + sub { + eval { + sub { + { + localize '$x' => 1 => $cxt; + # $cxt = SCOPE(0), or HERE + ... + } + # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0) + ... + }->(); + # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) + ... + }; + # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) + ... + }->(); + # $cxt = SCOPE(4), UP SUB UP SUB, or UP SUB EVAL, or UP CALLER(2), or TOP + ... + + Where "unwind" and "want_at" point to depending on the $cxt: + + sub { + eval { + sub { + { + unwind @things => $cxt; + ... + } + ... + }->(); # $cxt = SCOPE(0 .. 1), or HERE, or UP, or SUB, or CALLER(0) + ... + }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) + ... + }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) + ... - localize '$x', \'foo' => 0; +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'. - will set $x to a reference to the string 'foo'. Other sigils behave - as if a glob was passed. + The constant "SU_THREADSAFE" is also only exported on request, + individually or by the tags ':consts' and ':all'. - The symbol is resolved when the actual localization takes place and - not when "localize" is called. This means that + Same goes for the words "TOP", "HERE", "UP", "SUB", "EVAL", "SCOPE" and + "CALLER" that are only exported on request, individually or by the tags + ':words' and ':all'. - sub tag { localize '$x', $_[0] => 1; } +CAVEATS + Be careful that local variables are restored in the reverse order in + which they were localized. Consider those examples: - will localize in the caller's namespace. + local $x = 0; + { + reap sub { print $x } => HERE; + local $x = 1; + ... + } + # prints '0' + ... + { + local $x = 1; + reap sub { $x = 2 } => HERE; + ... + } + # $x is 0 - "localize_elem $what, $key, $value, $level" - 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. + The first case is "solved" by moving the "local" before the "reap", and + the second by using "localize" instead of "reap". - "TOPLEVEL" - Returns the level that currently represents the highest scope. + 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. -EXPORT - The functions "reap", "localize", "localize_elem" and "TOPLEVEL" are - only exported on request, either individually or by the tags ':funcs' - and ':all'. + 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-related fixes. DEPENDENCIES XSLoader (standard since perl 5.006). SEE ALSO + "local" in perlfunc, "Temporary Values via local()" in perlsub. + Alias, Hook::Scope, Scope::Guard, Guard. + 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, "", . @@ -112,11 +410,16 @@ SUPPORT perldoc Scope::Upper + Tests code coverage report is available at + . + ACKNOWLEDGEMENTS Inspired by Ricardo Signes. + Thanks to Shawn M. Moore for motivation. + COPYRIGHT & LICENSE - Copyright 2008 Vincent Pit, all rights reserved. + Copyright 2008,2009,2010 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.