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local/lib/perl5/Sub/Uplevel.pm  view on Meta::CPAN

#pod call stack
#pod
#pod * if we find a call to uplevel, we need to keep searching upwards beyond the
#pod requested height at least by the amount of upleveling requested for that
#pod call to uplevel (from the Up_Frames stack set during the uplevel call)
#pod
#pod * additionally, we need to hide the uplevel subroutine call, too, so we search
#pod upwards one more level for each call to uplevel
#pod
#pod * when we've reached the top of the search, we want to return that frame
#pod in the call stack, i.e. the requested height plus any uplevel adjustments
#pod found during the search
#pod
#pod =end _dagolden
#pod
#pod =cut

    my $saw_uplevel = 0;
    my $adjust = 0;

    # walk up the call stack to fight the right package level to return;
    # look one higher than requested for each call to uplevel found
    # and adjust by the amount found in the Up_Frames stack for that call.
    # We *must* use CORE::caller here since we need the real stack not what 
    # some other override says the stack looks like, just in case that other
    # override breaks things in some horrible way
    my $test_caller;
    for ( my $up = 0; $up <= $height + $adjust; $up++ ) {
        $test_caller = scalar CORE::caller($up + 1);
        if( $test_caller && $test_caller eq __PACKAGE__ ) {
            # add one for each uplevel call seen
            # and look into the uplevel stack for the offset
            $adjust += 1 + $Up_Frames[$saw_uplevel];
            $saw_uplevel++;
        }
    }

    # For returning values, we pass through the call to the proxy caller
    # function, just at a higher stack level
    my @caller = $Caller_Proxy->($height + $adjust + 1);
    if ( CORE::caller() eq 'DB' ) {
        # Oops, redo picking up @DB::args
        package DB;
        @caller = $Sub::Uplevel::Caller_Proxy->($height + $adjust + 1);
    }

    return if ! @caller;                  # empty
    return $caller[0] if ! wantarray;     # scalar context
    return @_ ? @caller : @caller[0..2];  # extra info or regular
}

#pod =back
#pod
#pod =head1 EXAMPLE
#pod
#pod The main reason I wrote this module is so I could write wrappers
#pod around functions and they wouldn't be aware they've been wrapped.
#pod
#pod     use Sub::Uplevel;
#pod
#pod     my $original_foo = \&foo;
#pod
#pod     *foo = sub {
#pod         my @output = uplevel 1, $original_foo;
#pod         print "foo() returned:  @output";
#pod         return @output;
#pod     };
#pod
#pod If this code frightens you B<you should not use this module.>
#pod
#pod
#pod =head1 BUGS and CAVEATS
#pod
#pod Well, the bad news is uplevel() is about 5 times slower than a normal
#pod function call.  XS implementation anyone?  It also slows down every invocation
#pod of caller(), regardless of whether uplevel() is in effect.
#pod
#pod Sub::Uplevel overrides CORE::GLOBAL::caller temporarily for the scope of
#pod each uplevel call.  It does its best to work with any previously existing
#pod CORE::GLOBAL::caller (both when Sub::Uplevel is first loaded and within 
#pod each uplevel call) such as from Contextual::Return or Hook::LexWrap.  
#pod
#pod However, if you are routinely using multiple modules that override 
#pod CORE::GLOBAL::caller, you are probably asking for trouble.
#pod
#pod You B<should> load Sub::Uplevel as early as possible within your program.  As
#pod with all CORE::GLOBAL overloading, the overload will not affect modules that
#pod have already been compiled prior to the overload.  One module that often is
#pod unavoidably loaded prior to Sub::Uplevel is Exporter.  To forcibly recompile
#pod Exporter (and Exporter::Heavy) after loading Sub::Uplevel, use it with the
#pod ":aggressive" tag:
#pod
#pod     use Sub::Uplevel qw/:aggressive/;
#pod
#pod The private function C<Sub::Uplevel::_force_reload()> may be passed a list of
#pod additional modules to reload if ":aggressive" is not aggressive enough.  
#pod Reloading modules may break things, so only use this as a last resort.
#pod
#pod As of version 0.20, Sub::Uplevel requires Perl 5.6 or greater.
#pod
#pod =head1 HISTORY
#pod
#pod Those who do not learn from HISTORY are doomed to repeat it.
#pod
#pod The lesson here is simple:  Don't sit next to a Tcl programmer at the
#pod dinner table.
#pod
#pod =head1 THANKS
#pod
#pod Thanks to Brent Welch, Damian Conway and Robin Houston.
#pod
#pod See http://www.perl.com/perl/misc/Artistic.html
#pod
#pod =head1 SEE ALSO
#pod
#pod PadWalker (for the similar idea with lexicals), Hook::LexWrap, 
#pod Tcl's uplevel() at http://www.scriptics.com/man/tcl8.4/TclCmd/uplevel.htm
#pod
#pod =cut

1;

__END__

local/lib/perl5/Sub/Uplevel.pm  view on Meta::CPAN

Setting or changing the global after the module has been loaded will have
no effect.

=begin _private

So it has to work like this:

    Call stack               Actual     uplevel 1
CORE::GLOBAL::caller
Carp::short_error_loc           0
Carp::shortmess_heavy           1           0
Carp::croak                     2           1
try_croak                       3           2
uplevel                         4            
function_that_called_uplevel    5            
caller_we_want_to_see           6           3
its_caller                      7           4

So when caller(X) winds up below uplevel(), it only has to use  
CORE::caller(X+1) (to skip CORE::GLOBAL::caller).  But when caller(X)
winds up no or above uplevel(), it's CORE::caller(X+1+uplevel+1).

Which means I'm probably going to have to do something nasty like walk
up the call stack on each caller() to see if I'm going to wind up   
before or after Sub::Uplevel::uplevel().

=end _private

=begin _dagolden

I found the description above a bit confusing.  Instead, this is the logic
that I found clearer when CORE::GLOBAL::caller is invoked and we have to
walk up the call stack:

* if searching up to the requested height in the real call stack doesn't find
a call to uplevel, then we can return the result at that height in the
call stack

* if we find a call to uplevel, we need to keep searching upwards beyond the
requested height at least by the amount of upleveling requested for that
call to uplevel (from the Up_Frames stack set during the uplevel call)

* additionally, we need to hide the uplevel subroutine call, too, so we search
upwards one more level for each call to uplevel

* when we've reached the top of the search, we want to return that frame
in the call stack, i.e. the requested height plus any uplevel adjustments
found during the search

=end _dagolden

=back

=head1 EXAMPLE

The main reason I wrote this module is so I could write wrappers
around functions and they wouldn't be aware they've been wrapped.

    use Sub::Uplevel;

    my $original_foo = \&foo;

    *foo = sub {
        my @output = uplevel 1, $original_foo;
        print "foo() returned:  @output";
        return @output;
    };

If this code frightens you B<you should not use this module.>

=head1 BUGS and CAVEATS

Well, the bad news is uplevel() is about 5 times slower than a normal
function call.  XS implementation anyone?  It also slows down every invocation
of caller(), regardless of whether uplevel() is in effect.

Sub::Uplevel overrides CORE::GLOBAL::caller temporarily for the scope of
each uplevel call.  It does its best to work with any previously existing
CORE::GLOBAL::caller (both when Sub::Uplevel is first loaded and within 
each uplevel call) such as from Contextual::Return or Hook::LexWrap.  

However, if you are routinely using multiple modules that override 
CORE::GLOBAL::caller, you are probably asking for trouble.

You B<should> load Sub::Uplevel as early as possible within your program.  As
with all CORE::GLOBAL overloading, the overload will not affect modules that
have already been compiled prior to the overload.  One module that often is
unavoidably loaded prior to Sub::Uplevel is Exporter.  To forcibly recompile
Exporter (and Exporter::Heavy) after loading Sub::Uplevel, use it with the
":aggressive" tag:

    use Sub::Uplevel qw/:aggressive/;

The private function C<Sub::Uplevel::_force_reload()> may be passed a list of
additional modules to reload if ":aggressive" is not aggressive enough.  
Reloading modules may break things, so only use this as a last resort.

As of version 0.20, Sub::Uplevel requires Perl 5.6 or greater.

=head1 HISTORY

Those who do not learn from HISTORY are doomed to repeat it.

The lesson here is simple:  Don't sit next to a Tcl programmer at the
dinner table.

=head1 THANKS

Thanks to Brent Welch, Damian Conway and Robin Houston.

See http://www.perl.com/perl/misc/Artistic.html

=head1 SEE ALSO

PadWalker (for the similar idea with lexicals), Hook::LexWrap, 
Tcl's uplevel() at http://www.scriptics.com/man/tcl8.4/TclCmd/uplevel.htm

=for :stopwords cpan testmatrix url annocpan anno bugtracker rt cpants kwalitee diff irc mailto metadata placeholders metacpan

=head1 SUPPORT

=head2 Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker