Vim & Vision
[ #233 ] Context managers in Perl Permalink
Let's try to implement something like Python's with statement in Perl.
First, let's look at Python. Python lets you do something like this:
class controlled_execution:
def __enter__(self):
set things up
return thing
def __exit__(self, type, value, traceback):
tear things down
with controlled_execution() as thing:
some code
(code example stolen from effbot)
The idea is that when the with block exits, the __exit__ cleanup is automatically called. This is nice for dealing with files, for example:
with f = open("somefile"):
f.read()
... where the implicit __exit__ code closes the file for us.
Can we do this in Perl? Sure. We just don't have the luxury of using nicely named __enter__ and __exit__ functions. Here is an example:
package Dir;
use strict;
use warnings;
use Cwd;
sub cd {
my $dir = shift;
my $code = shift;
my $origdir = getcwd();
chdir($dir);
$code->();
chdir($origdir);
}
1;
Now the script that utilises it:
#!/usr/bin/env perl
use strict;
use warnings;
use Dir;
Dir::cd "..", sub {
my @files = glob("*");
print join("\n", @files);
};
This context manager is for "cd", which chages directory, runs all the code in the block, and as it exits it simply changes back to the original directory it was in. There you go! Simple context managers in Perl.
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