Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

Hook::LexWrap can do some deeply funky things. It has been particularly helpful to me when I've needed to add instrumentation to code during debugging and testing.

Consider the following class:

package Foo; sub new { bless {todo => 0, done => 0}, shift }; sub add { shift->{todo}++ }; sub remove { my $self = shift; $self->{todo}--; $self->{done}++; }; sub todo { shift->{todo} }; sub done { shift->{done} };

Nice and simple. Unless of course some bad classes break encapsulation:

package Bar; use base qw(Foo); # oops. $self->{done} not updated sub naughty_remove { shift->{todo}-- }; ... package Ni; use base qw(Foo); sub naughty_transfer { my ($to, $from) = @_; while ($from->todo) { $to->{todo}++; # oops. $from->{done} not updated $from->{todo}--; }; };

This kind of bug can be hard to locate in large classes. Wouldn't it be nice if we could ask perl to keep a lookout for where Foo objects are used incorrectly by a subroutine? Maybe something like this:

# Monitor the arguments of subroutines ... my $monitor = monitor_arg # ... in the following packages ... in_package => [ 'Foo', 'Bar', 'Ni' ], # ... where the argument isa Foo object matching => sub { ref($_[0]) && UNIVERSAL::isa($_[0], 'Foo') }, # ... and check that we didn't mess with the internals ... with => sub { my ($original, $current, $subroutine) = @_; my $removed = $original->todo - $current->todo; my $done = $current->done - $original->done; warn "removed item not added to done list in $subroutine\n" if $removed > 0 && $removed != $done; };

With the wonder of Hook::LexWrap we can :-)

use Carp; use Storable qw(dclone); use Hook::LexWrap; use Devel::Symdump; our $Monitoring; sub monitor_arg { my %param = @_; my ($matching, $in_package, $with) = map {$param{$_} or croak "need $_"} qw(matching in_package with); croak "called in void context" unless defined wantarray; my @wrappers; foreach my $subroutine (Devel::Symdump->functions(@$in_package)) { my ($original, @current); push @wrappers, wrap $subroutine, pre => sub { return if $Monitoring; local $Monitoring = 1; @current = grep { $matching->($_) } @_; $original = dclone(\@current); }, post => sub { return if $Monitoring; local $Monitoring = 1; foreach my $current (@current) { my $original = shift @$original; $with->($original, $current, $subroutine); } }; }; return \@wrappers; };

So running:

my $o = Bar->new; $o->add; $o->add; $o->naughty_remove; my $from = Foo->new(); $from->add; my $to = Ni->new; $to->naughty_transfer($from);

with the previously shown call to monitor_arg will give us

removed item not added to done list in Bar::naughty_remove removed item not added to done list in Ni::naughty_transfer

I'm sure you get the idea. What interesting things have you done with Hook::LexWrap?


In reply to Fun with Hook::LexWrap and code instrumentation by adrianh

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others drinking their drinks and smoking their pipes about the Monastery: (13)
    As of 2015-07-08 05:20 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (94 votes), past polls