hooks: set $_ to substructure pointed by current step

README.md

@@ -80,17 +80,20 @@ list of regular expressions. Empty hash or empty list for `keys` means all
 keys. Sequence in `keys` and `regs` lists defines result sequence. `keys`
 have higher priority than `regs`.
 
+Coderef step is a hook - subroutine which may filter and/or modify
+structure. Path as first argument and a stack (arrayref) of refs to traversed
+subsstructures as second passed to it when executed, $\_ set to current
+substructure. Some true (match) value or false (doesn't match) value expected
+as output.
+
 Sample:
 
     $spath = [
-        [1,7],              # first spep
-        {regs => qr/foo/}   # second step
+        [1,7],                      # first spep
+        {regs => qr/foo/}           # second step
+        sub { exists $_->{bar} }    # third step
     ];
 
-Since v0.50 hooks (coderefs) as steps supported. Path as first argument and
-stack of references (arrayref) as second passed to it when executed. Some true
-(match) value or false (doesn't match) value expected as output.
-
 See [Struct::Path::PerlStyle](https://metacpan.org/pod/Struct::Path::PerlStyle) if you're looking for human friendly path
 definition method.
 

lib/Struct/Path.pm

@@ -104,17 +104,20 @@ list of regular expressions. Empty hash or empty list for C<keys> means all
 keys. Sequence in C<keys> and C<regs> lists defines result sequence. C<keys>
 have higher priority than C<regs>.
 
+Coderef step is a hook - subroutine which may filter and/or modify
+structure. Path as first argument and a stack (arrayref) of refs to traversed
+subsstructures as second passed to it when executed, $_ set to current
+substructure. Some true (match) value or false (doesn't match) value expected
+as output.
+
 Sample:
 
     $spath = [
-        [1,7],              # first spep
-        {regs => qr/foo/}   # second step
+        [1,7],                      # first spep
+        {regs => qr/foo/}           # second step
+        sub { exists $_->{bar} }    # third step
     ];
 
-Since v0.50 hooks (coderefs) as steps supported. Path as first argument and
-stack of references (arrayref) as second passed to it when executed. Some true
-(match) value or false (doesn't match) value expected as output.
-
 See L<Struct::Path::PerlStyle> if you're looking for human friendly path
 definition method.
 
@@ -310,6 +313,7 @@ sub spath($$;@) {
                     delete ${$refs->[-1]}->{$_} if ($opts{delete} and $sc == $#{$spath});
                 }
             } elsif (ref $step eq 'CODE') {
+                local $_ = ${$refs->[-1]};
                 $step->($path, $refs) and push @next, $path, $refs;
             } else {
                 croak "Unsupported thing in the path, step #$sc";

t/10-spath-address.t

@@ -2,15 +2,15 @@
 use 5.006;
 use strict;
 use warnings;
-use Test::More tests => 36;
+use Test::More tests => 38;
 
 use Struct::Path qw(spath);
 
 use Storable qw(freeze);
 $Storable::canonical = 1;
 
 use lib "t";
-use _common qw($s_array $s_mixed);
+use _common qw($s_array $s_mixed t_dump);
 
 my (@r, $frozen_s);
 
@@ -258,5 +258,29 @@ is_deeply(
     "code refs in the path (grep defined)"
 );
 
+do {
+    local $_ = 'must remain unchanged';
+
+    my $data = [
+        { k => 'one', v => 1 },
+        { k => 'two', v => 2, s => { k => 1 } },
+        { k => 'two', v => 2, s => { k => 2 } },
+    ];
+
+    my $dfltvar = sub {
+        $_->{k} eq 'two' and
+            exists $_->{s} and $_->{s}->{k} < 2
+    };
+
+    @r = spath($data, [ [],$dfltvar,{keys => ['k','s']} ]);
+    is_deeply(
+        \@r,
+        [\'two',\{k => 1}],
+        '$_ usage'
+    ) || diag t_dump \@r;
+
+    is($_, 'must remain unchanged', 'Default var ($_) locality check');
+};
+
 # original structure must remain unchanged
 ok($frozen_s eq freeze($s_mixed));