This is 0.12

[perl/modules/Scope-Upper.git] / README

diff --git a/README b/README
index c6d5711fc1c48803145c44c8e5cc143497a5efa0..527b31b15d7386a6de85a95a87825fccb16ccdf8 100644 (file)
--- a/README
+++ b/README
@@ -2,52 +2,81 @@ NAME
     Scope::Upper - Act on upper scopes.
 
 VERSION
     Scope::Upper - Act on upper scopes.
 
 VERSION

-    Version 0.04
+    Version 0.12

 
 SYNOPSIS
 
 SYNOPSIS

-        package X;
+    "reap", "localize", "localize_elem", "localize_delete" and "WORDS" :

 
 

-        use Scope::Upper qw/reap localize localize_elem localize_delete/;
+        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 {
          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;
+        }

 
 

-         localize_delete '@ARGV', $#ARGV => 1; # delete last @ARGV element
+        # 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..."

 
 

-        package Z;
+          {
+           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->();
 
         use Scope::Upper qw/unwind want_at :words/;
 
         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;
         }
 
          unwind +(want_at($cx) ? @result : scalar @result) => $cx;
         }
 


@@ -55,26 +84,46 @@ SYNOPSIS
 
         sub zap {
          try {
 
         sub zap {
          try {

+          my @things = qw/a b c/;

           return @things; # returns to try() and then outside zap()
           return @things; # returns to try() and then outside zap()

-         }
+          # not reached
+         };
+         # not reached

         }
 
         }
 

-        my @what = zap(); # @what contains @things
+        my @stuff = zap(); # @stuff contains qw/a b c/
+        my $stuff = zap(); # $stuff contains 3

 
 DESCRIPTION
 
 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.
+    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
 
 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.
+
+    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.

 
 

-  "localize $what, $value, $level"
-    A "local" delayed to the time of first return into the $level-th upper
-    scope. $what can be :
+  "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
 
     *   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


@@ -87,29 +136,61 @@ FUNCTIONS
         syntax as "local $x = $value", i.e. $value isn't dereferenced. For
         example,
 
         syntax as "local $x = $value", i.e. $value isn't dereferenced. For
         example,
 

-            localize '$x', \'foo' => 0;
+            localize '$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
 
         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. This
-        means that
-
-            sub tag { localize '$x', $_[0] => 1; }
-
-        will localize in the caller's namespace.
-
-  "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.
-
-  "localize_delete $what, $key, $level"
-    Similiar to "localize", but for deleting variables or array/hash
-    elements. $what can be:
+        localization takes place and not when "localize" is called. Thus, if
+        the symbol name is not qualified, it will refer to the variable in
+        the package where the localization actually takes place and not in
+        the one where the "localize" call was compiled. For example,
+
+            {
+             package Scope;
+             sub new { localize '$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 glob, in which case $key is ignored and the call is equivalent to
         "local *x".


@@ -122,46 +203,145 @@ FUNCTIONS
         in the upper scope. It's actually more powerful, as &func won't even
         "exists" anymore. $key is ignored.
 
         in the upper scope. It's actually more powerful, as &func won't even
         "exists" anymore. $key is ignored.
 

-  "unwind @values, $level"
-    Returns @values *from* the context indicated by $level, i.e. from the
-    subroutine, eval or format just above $level. The upper level isn't
-    coerced onto @values, which is hence always evaluated in list context.
+  "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.

 
 

-  "want_at $level"
-    Like "wantarray", but for the subroutine/eval/format context just above
-    $level.
+    The upper context isn't coerced onto @values, which is hence always
+    evaluated in list context. This means that

 
 

-WORDS
-  "TOP"
-    Returns the level that currently represents the highest scope.
+        my $num = sub {
+         my @a = ('a' .. 'z');
+         unwind @a => HERE;
+         # not reached
+        }->();

 
 

-  "HERE"
-    The current level - i.e. 0.
+    will set $num to 'z'. You can use "want_at" to handle these cases.

 
 

-  "UP $from"
-    The level of the scope just above $from.
+  "want_at $context"
+    Like "wantarray", but for the subroutine/eval/format at or just above
+    $context.

 
 

-  "DOWN $from"
-    The level of the scope just below $from.
+    The previous example can then be "corrected" :

 
 

-  "SUB $from"
-    The level of the closest subroutine context above $from.
+        my $num = sub {
+         my @a = ('a' .. 'z');
+         unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
+         # not reached
+        }->();

 
 

-  "EVAL $from"
-    The level of the closest eval context above $from.
+    will rightfully set $num to 26.

 
 

-    If $from is omitted in any of those functions, the current level is used
-    as the reference level.
+CONSTANTS
+  "SU_THREADSAFE"
+    True iff the module could have been built when thread-safety features.

 
 

-  "CALLER $stack"
-    The level corresponding to the stack referenced by "caller $stack".
+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)
+        ...

 
 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'.
 
 
 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'.
 

-    Same goes for the words "TOP", "HERE", "UP", "DOWN", "SUB", "EVAL" and
+    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
     ':words' and ':all'.
 
     "CALLER" that are only exported on request, individually or by the tags
     ':words' and ':all'.
 


@@ -171,7 +351,7 @@ CAVEATS
 
         local $x = 0;
         {
 
         local $x = 0;
         {

-         reap sub { print $x } => 0;
+         reap sub { print $x } => HERE;

          local $x = 1;
          ...
         }
          local $x = 1;
          ...
         }


@@ -179,7 +359,7 @@ CAVEATS
         ...
         {
          local $x = 1;
         ...
         {
          local $x = 1;

-         reap sub { $x = 2 } => 0;
+         reap sub { $x = 2 } => HERE;

          ...
         }
         # $x is 0
          ...
         }
         # $x is 0


@@ -187,17 +367,32 @@ CAVEATS
     The first case is "solved" by moving the "local" before the "reap", and
     the second by using "localize" instead of "reap".
 
     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.
     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-related fixes.

 
 DEPENDENCIES
     XSLoader (standard since perl 5.006).
 
 SEE ALSO
 
 DEPENDENCIES
     XSLoader (standard since perl 5.006).
 
 SEE ALSO

+    "local" in perlfunc, "Temporary Values via local()" in perlsub.
+

     Alias, Hook::Scope, Scope::Guard, Guard.
 
     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, "<perl at profvince.com>", <http://www.profvince.com>.
 
 AUTHOR
     Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
 


@@ -221,8 +416,10 @@ SUPPORT
 ACKNOWLEDGEMENTS
     Inspired by Ricardo Signes.
 
 ACKNOWLEDGEMENTS
     Inspired by Ricardo Signes.
 

+    Thanks to Shawn M. Moore for motivation.
+

 COPYRIGHT & LICENSE
 COPYRIGHT & LICENSE

-    Copyright 2008-2009 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.
 
     This program is free software; you can redistribute it and/or modify it
     under the same terms as Perl itself.