X-Git-Url: http://git.vpit.fr/?a=blobdiff_plain;f=lib%2FScope%2FUpper.pm;h=b5936dbfa325253e1d2625c83205d71055c33cb7;hb=70187dc24bb0f90a81f58ff2bd52ba7d9c3ac06f;hp=6128a8f10dd0fb906ca2663fa89215acffbd584b;hpb=ded0c62307dd417bbd7390457692310aca67ea93;p=perl%2Fmodules%2FScope-Upper.git

diff --git a/lib/Scope/Upper.pm b/lib/Scope/Upper.pm
index 6128a8f..b5936db 100644
--- a/lib/Scope/Upper.pm
+++ b/lib/Scope/Upper.pm
@@ -9,58 +9,187 @@ Scope::Upper - Act on upper scopes.
 
 =head1 VERSION
 
-Version 0.01
+Version 0.18
 
 =cut
 
 our $VERSION;
 BEGIN {
- $VERSION = '0.01';
+ $VERSION = '0.18';
 }
 
 =head1 SYNOPSIS
 
-    package X;
+L</reap>, L</localize>, L</localize_elem>, L</localize_delete> and L</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;
+    }
+
+    # 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
-     warn 'what'; # warns "pie: what at ..."
+     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"
+
+L</unwind> and L</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
+
+L</uplevel> :
+
+    package Uplevel;
+
+    use Scope::Upper qw<uplevel CALLER>;
+
+    sub target {
+     faker(@_);
+    }
+
+    sub faker {
+     uplevel {
+      my $sub = (caller 0)[3];
+      print "$_[0] from $sub()";
+     } @_ => CALLER(1);
+    }
+
+    target('hello'); # "hello from Uplevel::target()"
+
+L</uid> and L</validate_uid> :
+
+    use Scope::Upper qw<uid validate_uid>;
+
+    my $uid;
+
+    {
+     $uid = uid();
+     {
+      if ($uid eq uid(UP)) { # yes
+       ...
+      }
+      if (validate_uid($uid)) { # yes
+       ...
+      }
+     }
+    }
+
+    if (validate_uid($uid)) { # no
      ...
-    } # "pie: done" is printed
+    }
 
 =head1 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 I<at run-time> that will take place when the control flow returns into an upper scope.
+Currently, you can:
+
+=over 4
+
+=item *
+
+hook an upper scope end with L</reap> ;
+
+=item *
+
+localize variables, array/hash values or deletions of elements in higher contexts with respectively L</localize>, L</localize_elem> and L</localize_delete> ;
+
+=item *
+
+return values immediately to an upper level with L</unwind>, and know which context was in use then with L</want_at> ;
+
+=item *
+
+execute a subroutine in the setting of an upper subroutine stack frame with L</uplevel> ;
+
+=item *
+
+uniquely identify contextes with L</uid> and L</validate_uid>.
+
+=back
 
 =head1 FUNCTIONS
 
+In all those functions, C<$context> refers to the target scope.
+
+You have to use one or a combination of L</WORDS> to build the C<$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 I<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.
+
 =cut
 
 BEGIN {
@@ -68,13 +197,13 @@ BEGIN {
  XSLoader::load(__PACKAGE__, $VERSION);
 }
 
-=head2 C<reap $callback, $level>
+=head2 C<reap $callback, $context>
 
-Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
+Adds a destructor that calls C<$callback> (in void context) when the upper scope represented by C<$context> ends.
 
-=head2 C<localize $what, $value, $level>
+=head2 C<localize $what, $value, $context>
 
-A C<local> delayed to the time of first return into the C<$level>-th upper scope.
+Introduces a C<local> delayed to the time of first return into the upper scope denoted by C<$context>.
 C<$what> can be :
 
 =over 4
@@ -91,53 +220,443 @@ A string beginning with a sigil, representing the symbol to localize and to assi
 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
 For example,
 
-    localize '$x', \'foo' => 0;
+    localize '$x', \'foo' => HERE;
 
 will set C<$x> to a reference to the string C<'foo'>.
 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$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 C<localize> is called.
-This means that
+When the symbol is given by a string, it is resolved when the actual localization takes place and not when L</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 L</localize> call was compiled.
+For example,
+
+    {
+     package Scope;
+     sub new { localize '$tag', $_[0] => UP }
+    }
+
+    {
+     package Tool;
+     {
+      Scope->new;
+      ...
+     }
+    }
 
-    sub tag { localize '$x', $_[0] => 1; }
+will localize C<$Tool::tag> and not C<$Scope::tag>.
+If you want the other behaviour, you just have to specify C<$what> as a glob or a qualified name.
 
-will localize in the caller's namespace.
+Note that if C<$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 C<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.
 
 =back
 
-=head2 C<localize_elem $what, $key, $value, $level>
+=head2 C<localize_elem $what, $key, $value, $context>
 
-Similar to L</localize> but for array and hash elements.
-If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
+Introduces a C<local $what[$key] = $value> or C<local $what{$key} = $value> delayed to the time of first return into the upper scope denoted by C<$context>.
+Unlike L</localize>, C<$what> must be a string and the type of localization is inferred from its sigil.
+The two only valid types are array and hash ; for anything besides those, L</localize_elem> will throw an exception.
 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
 
-=head2 C<TOPLEVEL>
+If C<$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.
+
+=head2 C<localize_delete $what, $key, $context>
+
+Introduces the deletion of a variable or an array/hash element delayed to the time of first return into the upper scope denoted by C<$context>.
+C<$what> can be:
+
+=over 4
+
+=item *
+
+A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
+
+=item *
+
+A string beginning with C<'@'> or C<'%'>, for which the call is equivalent to respectiveley C<local $a[$key]; delete $a[$key]> and C<local $h{$key}; delete $h{$key}>.
+
+=item *
+
+A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
+It's actually more powerful, as C<&func> won't even C<exists> anymore.
+C<$key> is ignored.
 
-Returns the level that currently represents the highest scope.
+=back
+
+=head2 C<unwind @values, $context>
+
+Returns C<@values> I<from> the context pointed by C<$context>, i.e. from the subroutine, eval or format at or just above C<$context>, and immediately restart the program flow at this point - thus effectively returning to an upper scope.
+
+The upper context isn't coerced onto C<@values>, which is hence always evaluated in list context.
+This means that
+
+    my $num = sub {
+     my @a = ('a' .. 'z');
+     unwind @a => HERE;
+     # not reached
+    }->();
+
+will set C<$num> to C<'z'>.
+You can use L</want_at> to handle these cases.
+
+=head2 C<want_at $context>
+
+Like C<wantarray>, but for the subroutine/eval/format at or just above C<$context>.
+
+The previous example can then be "corrected" :
+
+    my $num = sub {
+     my @a = ('a' .. 'z');
+     unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
+     # not reached
+    }->();
+
+will rightfully set C<$num> to C<26>.
+
+=head2 C<uplevel $code, @args, $context>
+
+Executes the code reference C<$code> with arguments C<@args> as if it were located at the subroutine stack frame pointed by C<$context>, effectively fooling C<caller> and C<die> into believing that the call actually happened higher in the stack.
+The code is executed in the context of the C<uplevel> call, and what it returns is returned as-is by C<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
+
+L<Sub::Uplevel> also implements a pure-Perl version of C<uplevel>.
+Both are identical, with the following caveats :
+
+=over 4
+
+=item *
+
+The L<Sub::Uplevel> implementation of C<uplevel> may execute a code reference in the context of B<any> upper stack frame.
+The L<Scope::Upper> version can only uplevel to a B<subroutine> stack frame, and will croak if you try to target an C<eval> or a format.
+
+=item *
+
+Exceptions thrown from the code called by this version of C<uplevel> will not be caught by C<eval> blocks between the target frame and the uplevel call, while they will for L<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 L<Sub::Uplevel> and "outer block: wut..." with L<Scope::Upper>.
+
+=item *
+
+L<Sub::Uplevel> globally overrides the Perl keyword C<caller>, while L<Scope::Upper> does not.
+
+=back
+
+A simple wrapper lets you mimic the interface of L<Sub::Uplevel/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 L<Sub::Uplevel>.
+
+=head2 C<uid $context>
+
+Returns an unique identifier (UID) for the context (or dynamic scope) pointed by C<$context>, or for the current context if C<$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 C<eq> operator to compare them.
+
+To check whether a given UID is valid, you can use the L</validate_uid> function.
+
+=head2 C<validate_uid $uid>
+
+Returns true if and only if C<$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
+     ...
+    }
+
+=head1 CONSTANTS
+
+=head2 C<SU_THREADSAFE>
+
+True iff the module could have been built when thread-safety features.
+
+=head1 WORDS
+
+=head2 Constants
+
+=head3 C<TOP>
+
+Returns the context that currently represents the highest scope.
+
+=head3 C<HERE>
+
+The context of the current scope.
+
+=head2 Getting a context from a context
+
+For any of those functions, C<$from> is expected to be a context.
+When omitted, it defaults to the the current context.
+
+=head3 C<UP $from>
+
+The context of the scope just above C<$from>.
+
+=head3 C<SUB $from>
+
+The context of the closest subroutine above C<$from>.
+Note that C<$from> is returned if it is already a subroutine context ; hence C<SUB SUB == SUB>.
+
+=head3 C<EVAL $from>
+
+The context of the closest eval above C<$from>.
+Note that C<$from> is returned if it is already an eval context ; hence C<EVAL EVAL == EVAL>.
+
+=head2 Getting a context from a level
+
+Here, C<$level> should denote a number of scopes above the current one.
+When omitted, it defaults to C<0> and those functions return the same context as L</HERE>.
+
+=head3 C<SCOPE $level>
+
+The C<$level>-th upper context, regardless of its type.
+
+=head3 C<CALLER $level>
+
+The context of the C<$level>-th upper subroutine/eval/format.
+It kind of corresponds to the context represented by C<caller $level>, but while e.g. C<caller 0> refers to the caller context, C<CALLER 0> will refer to the top scope in the current context.
+
+=head2 Examples
+
+Where L</reap> fires depending on the C<$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)
+     ...
+    }->();   # $cxt = SCOPE(3) = SUB UP SUB = SUB EVAL = CALLER(2)
+    ...
+
+Where L</localize>, L</localize_elem> and L</localize_delete> act depending on the C<$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)
+     ...
+    }->();
+    # $cxt = SCOPE(4), UP SUB UP SUB = UP SUB EVAL = UP CALLER(2) = TOP
+    ...
+
+Where L</unwind>, L</want_at> and L</uplevel> point to depending on the C<$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.
 
 =head1 EXPORT
 
-The functions L</reap>, L</localize>, L</localize_elem> and L</TOPLEVEL> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
+The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>,  L</unwind>, L</want_at> and L</uplevel> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
+
+The constant L</SU_THREADSAFE> is also only exported on request, individually or by the tags C<':consts'> and C<':all'>.
+
+Same goes for the words L</TOP>, L</HERE>, L</UP>, L</SUB>, L</EVAL>, L</SCOPE> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
 
 =cut
 
-use base qw/Exporter/;
+use base qw<Exporter>;
 
 our @EXPORT      = ();
 our %EXPORT_TAGS = (
- funcs => [ qw/reap localize localize_elem TOPLEVEL/ ],
+ funcs  => [ qw<
+  reap
+  localize localize_elem localize_delete
+  unwind want_at
+  uplevel
+  uid validate_uid
+ > ],
+ words  => [ qw<TOP HERE UP SUB EVAL SCOPE CALLER> ],
+ consts => [ qw<SU_THREADSAFE> ],
 );
 our @EXPORT_OK   = map { @$_ } values %EXPORT_TAGS;
 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
 
+=head1 CAVEATS
+
+Be careful that local variables are restored in the reverse order in which they were localized.
+Consider those examples:
+
+    local $x = 0;
+    {
+     reap sub { print $x } => HERE;
+     local $x = 1;
+     ...
+    }
+    # prints '0'
+    ...
+    {
+     local $x = 1;
+     reap sub { $x = 2 } => HERE;
+     ...
+    }
+    # $x is 0
+
+The first case is "solved" by moving the C<local> before the C<reap>, and the second by using L</localize> instead of L</reap>.
+
+The effects of L</reap>, L</localize> and L</localize_elem> can't cross C<BEGIN> blocks, hence calling those functions in C<import> is deemed to be useless.
+This is an hopeless case because C<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 L<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-related fixes.
+
+Calling C<goto> to replace an L</uplevel>'d code frame does not work :
+
+=over 4
+
+=item *
+
+for a C<perl> older than the 5.8 series ;
+
+=item *
+
+for a C<DEBUGGING> C<perl> run with debugging flags set (as in C<perl -D ...>) ;
+
+=item *
+
+when the runloop callback is replaced by another module.
+
+=back
+
+In those three cases, L</uplevel> will look for a C<goto &sub> statement in its callback and, if there is one, throw an exception before executing the code.
+
+Moreover, in order to handle C<goto> statements properly, L</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 B<all> the code executed as the result of the L</uplevel> call (including subroutine calls inside the callback) when a C<goto> statement is found in the L</uplevel> callback.
+Despite this shortcoming, this XS version of L</uplevel> should still run way faster than the pure-Perl version from L<Sub::Uplevel>.
+
 =head1 DEPENDENCIES
 
 L<XSLoader> (standard since perl 5.006).
 
 =head1 SEE ALSO
 
+L<perlfunc/local>, L<perlsub/"Temporary Values via local()">.
+
 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
 
+L<Sub::Uplevel>.
+
+L<Continuation::Escape> is a thin wrapper around L<Scope::Upper> that gives you a continuation passing style interface to L</unwind>.
+It's easier to use, but it requires you to have control over the scope where you want to return.
+
+L<Scope::Escape>.
+
 =head1 AUTHOR
 
 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
@@ -146,7 +665,8 @@ You can contact me by mail or on C<irc.perl.org> (vincent).
 
 =head1 BUGS
 
-Please report any bugs or feature requests to C<bug-scope-upper at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Scope-Upper>.  I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
+Please report any bugs or feature requests to C<bug-scope-upper at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Scope-Upper>.
+I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
 
 =head1 SUPPORT
 
@@ -154,13 +674,17 @@ You can find documentation for this module with the perldoc command.
 
     perldoc Scope::Upper
 
+Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
+
 =head1 ACKNOWLEDGEMENTS
 
 Inspired by Ricardo Signes.
 
+Thanks to Shawn M. Moore for motivation.
+
 =head1 COPYRIGHT & LICENSE
 
-Copyright 2008 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.