Tying with a class method

ninja-joe has asked for the wisdom of the Perl Monks concerning the following question:

Suppose I have a class, and I want to have a persistent tie to a dbm file. I'm using strict also. I want to have two subs, a connect and disconnect. If I were to do

sub connect {
     my $self = shift;
     tie %data, "AnyDBM_File", "data", O_RDWR, 0644
          or die "Cannot open data for read.\n";
     return 1;
}

sub disconnect {
     untie %data;
}
[download]

Would it work the way I'd hope it would? Or would the tie to data be lost because of the scope of the sub? Could I then do something like

sub data {
     my $self = shift;
     my $bar = shift;

     if(@_) {
          $data{$bar} = $self->{FOO};
     }
}
[download]

And expect it to behave correctly? Perhaps it would be better to tie the dbm file to a class member, but I don't know how one would do that.

Comment on Tying with a class method Select or Download Code

Replies are listed 'Best First'.
Re: Tying with a class method by broquaint (Abbot) on May 02, 2002 at 15:24 UTC
If `%data` is visible to both `connect()` and `disconnect()` then it should work as expected (e.g if `%data` is a pacakge variable). However if you'd still like to use lexical variables and have it visible to both functions you could use closure behaviour `{ my %data; sub connect { my $self = shift; tie %data, "AnyDBM_File", "data", O_RDWR, 0644 or die "Cannot open data for read.\n"; return 1; } sub disconnect { untie %data; } } # %data has fallen out of scope and only exists # within connect() and disconnect()` [download] So `%data` would now be within the scope of both the subs, and nothing else. Unfortunately this would trip up `data()`, but you could also include that within the block that `connect()` and `disconnect()` are in. For more info on closures check out Why Closures? and other related notes. HTH `_________ broquaint`	[reply] [d/l]
Re: Re: Tying with a class method by ninja-joe (Monk) on May 02, 2002 at 16:49 UTC
I was under the impression that "use strict" would disallow me from using package level variables. I'm probably wrong though. Suppose if I wanted to make a hash a member of that class, regardless of whether strict minded or not, would it just work like: `$self->hash{"foo"} = "bar";` and `%self->hash` ? Where I'd be able to do a statement such as `tie %self->hash, "AnyDBM_File", "data", O_RDWR, 0644;` [download]	[reply] [d/l] [select]
Re: Re: Re: Tying with a class method by broquaint (Abbot) on May 02, 2002 at 17:09 UTC
I was under the impression that "use strict" would disallow me from using package level variables The use of `strict` merely discourages the use of package variables. As long as a variable exists within the package's symbol table you're free to use it without it being fully qualifying. If you had a hash as a data member of the blessed object (which itself was a hash) then you would use it like so `# assign to hash $self->{hash}->{foo} = 'bar'; # get keys from hash keys %{$self->{hash}}; # tie hash tie %{$self->{hash}}, "AnyDBM_File", "data", O_RDWR, 0644;` [download] If you're a little confused about how how classes and objects work I'd recommend reading Tom Christiansen's oo tutorial and perhaps also read up on references in perl. HTH `_________ broquaint`	[reply] [d/l]


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