view release on metacpan or  search on metacpan

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

      require Carp;
      Carp::carp("uplevel $_[0] is more than the caller stack");
    }

    local @Up_Frames = (shift, @Up_Frames );

    my $function = shift;
    return $function->(@_);
}

sub _normal_caller (;$) { ## no critic Prototypes
    my ($height) = @_;
    $height++;
    my @caller = CORE::caller($height);
    if ( CORE::caller() eq 'DB' ) {
        # Oops, redo picking up @DB::args
        package DB;
        @caller = CORE::caller($height);
    }

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

sub _uplevel_caller (;$) { ## no critic Prototypes
    my $height = $_[0] || 0;

    # shortcut if no uplevels have been called
    # always add +1 to CORE::caller (proxy caller function)
    # to skip this function's caller
    return $Caller_Proxy->( $height + 1 ) if ! @Up_Frames;

#pod =begin _private
#pod
#pod So it has to work like this:
#pod
#pod     Call stack               Actual     uplevel 1
#pod CORE::GLOBAL::caller
#pod Carp::short_error_loc           0
#pod Carp::shortmess_heavy           1           0
#pod Carp::croak                     2           1
#pod try_croak                       3           2
#pod uplevel                         4            
#pod function_that_called_uplevel    5            
#pod caller_we_want_to_see           6           3
#pod its_caller                      7           4
#pod
#pod So when caller(X) winds up below uplevel(), it only has to use  
#pod CORE::caller(X+1) (to skip CORE::GLOBAL::caller).  But when caller(X)
#pod winds up no or above uplevel(), it's CORE::caller(X+1+uplevel+1).
#pod
#pod Which means I'm probably going to have to do something nasty like walk
#pod up the call stack on each caller() to see if I'm going to wind up   
#pod before or after Sub::Uplevel::uplevel().
#pod
#pod =end _private
#pod
#pod =begin _dagolden
#pod
#pod I found the description above a bit confusing.  Instead, this is the logic
#pod that I found clearer when CORE::GLOBAL::caller is invoked and we have to
#pod walk up the call stack:
#pod
#pod * if searching up to the requested height in the real call stack doesn't find
#pod a call to uplevel, then we can return the result at that height in the
#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

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

    sub wrapper {
        print "Before\n";
        goto &some_func;
        print "After\n";
    }

you can do this:

    sub wrapper {
        print "Before\n";
        my @out = uplevel 1, &some_func;
        print "After\n";
        return @out;
    }

C<uplevel> has the ability to issue a warning if C<$num_frames> is more than
the current call stack depth, although this warning is disabled and compiled
out by default as the check is relatively expensive.

To enable the check for debugging or testing, you should set the global
C<$Sub::Uplevel::CHECK_FRAMES> to true before loading Sub::Uplevel for the
first time as follows:

    #!/usr/bin/perl
    
    BEGIN {
        $Sub::Uplevel::CHECK_FRAMES = 1;
    }
    use Sub::Uplevel;

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: