Beefy Boxes and Bandwidth Generously Provided by pair Networks
P is for Practical
 
PerlMonks  

tied file handle, extra variable?

by live4tech (Sexton)
on Jan 06, 2013 at 08:22 UTC ( #1011847=perlquestion: print w/ replies, xml ) Need Help??
live4tech has asked for the wisdom of the Perl Monks concerning the following question:

I wish a good start to the new year to everyone!

I have been reading Damian Conway's Object Oriented Perl book. I have enjoyed it for the most part especially the beginning chapters where I think he does a good job of covering some perl basics. After that, the book is a bit of a struggle probably because I am new to perl and because this book is from 2000 and some of it is definitely out of date. In any case the following code has me perplexed:

sub TIEHANDLE { my ($class, %args) = @_; my $handle = gensym(); my $impl = bless { handle => gensym() }, $class; $impl->OPEN (%args); return $impl; } sub OPEN { my ($impl, %args) = @_; open $impl->{handle}, $args{file} or croak "Could not open '$args{f +ile}'"; $impl->{in_filter} = $args{in} || \&_no_filter; $impl->{out_filter} = $args{out} || \&_no_filter; }

I am confused by something in the subroutine TIEHANDLE. Here is what I think is going on:

The class name ($class) is taken from the list of parameters passed to the subroutine. A hash (%args) is taken from the rest of the parameter list.

Then $handle is assigned to an anonymous glob and therefore becomes a reference to a type glob.

Then $impl is initialized as an object (blessed into the package) referencing an anonymous hash with a key "handle" and value gensym() (creating another reference to a glob).

Then the method OPEN is called using $impl->OPEN (%args)

The $impl object is then returned.

My question is, why do we need the reference "$handle" in the line "my $handle = gensym()"? This reference is not used after this line. In fact a new glob reference is created in the next line in the hash which is blessed. Why do we need $handle at all here? Also I have read the gensym() perldoc and it looks like it is not used anymore although that document is difficult to understand.

Comment on tied file handle, extra variable?
Download Code
Re: tied file handle, extra variable?
by BrowserUk (Pope) on Jan 06, 2013 at 08:51 UTC
    Why do we need $handle at all here?

    You don't. Its a typo/thinko/edito.


    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
Re: tied file handle, extra variable?
by Anonymous Monk on Jan 06, 2013 at 09:19 UTC

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://1011847]
Approved by BrowserUk
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others avoiding work at the Monastery: (7)
As of 2014-12-21 22:21 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    Is guessing a good strategy for surviving in the IT business?





    Results (108 votes), past polls