Improved synopsys

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

diff --git a/README b/README
index feecd5c772b15f2e41961756e0e81892159d3834..074581cbe7cf8130d2d391cbbc85974e775d7b8f 100644 (file)
--- a/README
+++ b/README
@@ -2,12 +2,12 @@ NAME
     Scope::Upper - Act on upper scopes.
 
 VERSION
     Scope::Upper - Act on upper scopes.
 
 VERSION

-    Version 0.05
+    Version 0.10

 
 SYNOPSIS
         package X;
 
 
 SYNOPSIS
         package X;
 

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

 
         sub desc { shift->{desc} }
 
 
         sub desc { shift->{desc} }
 


@@ -15,21 +15,22 @@ SYNOPSIS
          my ($desc) = @_;
 
          # First localize $x so that it gets destroyed last
          my ($desc) = @_;
 
          # First localize $x so that it gets destroyed last

-         localize '$x' => bless({ desc => $desc }, __PACKAGE__) => 1;
+         localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP; # one scope 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";
 
          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;
+         } => SCOPE 1; # same as UP here

 
          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('', @_));
 
          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;
+         } => UP CALLER 0; # same as UP here

 
 

-         localize_delete '@ARGV', $#ARGV => 1; # delete last @ARGV element
+         # delete last @ARGV element
+         localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here

         }
 
         package Y;
         }
 
         package Y;


@@ -56,26 +57,43 @@ SYNOPSIS
         sub zap {
          try {
           return @things; # returns to try() and then outside zap()
         sub zap {
          try {
           return @things; # returns to try() and then outside zap()

+          # not reached

          }
          }

+         # not reached

         }
 
         my @what = zap(); # @what contains @things
 
 DESCRIPTION
         }
 
         my @what = zap(); # @what contains @things
 
 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".

 
 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.
+
+  "reap $callback, $context"
+    Add a destructor that calls $callback (in void context) when the upper
+    scope represented by $context ends.

 
 

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


@@ -88,7 +106,7 @@ 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
 
         will set $x to a reference to the string 'foo'. Other sigils ('@',
         '%', '&' and '*') require $value to be a reference of the


@@ -98,17 +116,17 @@ FUNCTIONS
         localization takes place and not when "localize" is called. This
         means that
 
         localization takes place and not when "localize" is called. This
         means that
 

-            sub tag { localize '$x', $_[0] => 1; }
+            sub tag { localize '$x', $_[0] => UP }

 
         will localize in the caller's namespace.
 
 
         will localize in the caller's namespace.
 

-  "localize_elem $what, $key, $value, $level"
+  "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.
 
     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"
+  "localize_delete $what, $key, $context"

     Similiar to "localize", but for deleting variables or array/hash
     elements. $what can be:
 
     Similiar to "localize", but for deleting variables or array/hash
     elements. $what can be:
 


@@ -123,71 +141,145 @@ 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.
+  "unwind @values, $context"
+    Returns @values *from* the context pointed by $context, i.e. from the
+    subroutine, eval or format just above $context, and immediately restart
+    the program flow at this point - thus effectively returning to (or from,
+    depending on how you see it) an upper context.

 
 

-    The upper level isn't coerced onto @values, which is hence always
+    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');
     evaluated in list context. This means that
 
         my $num = sub {
          my @a = ('a' .. 'z');

-         unwind @a => 0;
+         unwind @a => HERE;
+         # not reached

         }->();
 
     will set $num to 'z'. You can use "want_at" to handle these cases.
 
         }->();
 
     will set $num to 'z'. You can use "want_at" to handle these cases.
 

-  "want_at $level"
-    Like "wantarray", but for the subroutine/eval/format context just above
-    $level.
+  "want_at $context"
+    Like "wantarray", but for the subroutine/eval/format just above
+    $context.

 
     The previous example can then be "corrected" :
 
         my $num = sub {
          my @a = ('a' .. 'z');
 
     The previous example can then be "corrected" :
 
         my $num = sub {
          my @a = ('a' .. 'z');

-         unwind +(want_at(0) ? @a : scalar @a) => 0;
+         unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
+         # not reached

         }->();
 
         }->();
 

-    will righteously set $num to 26.
+    will rightfully set $num to 26.
+
+CONSTANTS
+  "SU_THREADSAFE"
+    True iff the module could have been built when thread-safety features.

 
 WORDS
 
 WORDS

-  "TOP"
-    Returns the level that currently represents the highest scope.
+  Constants
+   "TOP"
+    Returns the context that currently represents the highest scope.
+
+   "HERE"
+    The context of the current scope.

 
 

-  "HERE"
-    The current level - i.e. 0.
+  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 level of the scope just above $from.
+   "UP $from"
+    The context of the scope just above $from.

 
 

-  "DOWN $from"
-    The level of the scope just below $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".

 
 

-  "SUB $from"
-    The level of the closest subroutine context above $from.
+   "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".

 
 

-  "EVAL $from"
-    The level of the closest eval context above $from.
+  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".

 
 

-    If $from is omitted in any of those functions, the current level is used
-    as the reference level.
+   "SCOPE $level"
+    The $level-th upper context, regardless of its type.

 
 

-  "CALLER $stack"
-    The level of the $stack-th upper subroutine/eval/format context. It kind
-    of corresponds to the context represented by "caller $stack", but while
+   "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
     e.g. "caller 0" refers to the caller context, "CALLER 0" will refer to

-    the top scope in the current context. For example,
+    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)
+        ...

 
 

-        reap ... => CALLER(0)
+    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
+        ...

 
 

-    will fire the destructor when the current subroutine/eval/format ends.
+    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'.
 


@@ -197,7 +289,7 @@ CAVEATS
 
         local $x = 0;
         {
 
         local $x = 0;
         {

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

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


@@ -205,7 +297,7 @@ CAVEATS
         ...
         {
          local $x = 1;
         ...
         {
          local $x = 1;

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

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


@@ -213,10 +305,16 @@ 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).
 
 DEPENDENCIES
     XSLoader (standard since perl 5.006).


@@ -224,6 +322,11 @@ DEPENDENCIES
 SEE ALSO
     Alias, Hook::Scope, Scope::Guard, Guard.
 
 SEE ALSO
     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.
+

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


@@ -247,8 +350,10 @@ 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.