Automatically release resources RAII-style in Perl
- by Philip Potter
Say I have a resource (e.g. a filehandle or network socket) which has to be freed:
open my $fh, "<", "filename" or die "Couldn't open filename: $!";
process($fh);
close $fh or die "Couldn't close filename: $!";
Suppose that process might die. Then the code block exits early, and $fh doesn't get closed.
I could explicitly check for errors:
open my $fh, "<", "filename" or die "Couldn't open filename: $!";
eval {process($fh)};
my $saved_error = $@;
close $fh or die "Couldn't close filename: $!";
die $saved_error if $saved_error;
but this kind of code is notoriously difficult to get right, and only gets more complicated when you add more resources.
In C++ I would use RAII to create an object which owns the resource, and whose destructor would free it. That way, I don't have to remember to free the resource, and resource cleanup happens correctly as soon as the RAII object goes out of scope - even if an exception is thrown. Unfortunately in Perl a DESTROY method is unsuitable for this purpose as there are no guarantees for when it will be called.
Is there a Perlish way to ensure resources are automatically freed like this even in the presence of exceptions? Or is explicit error checking the only option?
