Here's a simple one I use, to locally override something:

package MyApp::Local;
use strict;

sub umask {
  my($class, $umask) = @_;
  my $old = umask $umask;
  $class->new(sub { umask $old });
}

# ... and various other more application-specific methods

sub new {
  my($class, $cb) = @_;
  bless $cb, $class;
}

sub DESTROY {
  my $self = shift;
  $self->();
  undef;
}

1;
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Example use:

  ...
  {
    # create the file, must be world-writable
    my $temp = MyApp::Local->umask(0);
    my $fh;
    sysopen($fh, $path, O_WRONLY | O_CREAT | O_EXCL, 0666)
        or die "$path: $!\n";
    close $fh;
    # umask restored when $temp goes out of scope, even by dying
  }
  ...
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No particular reason this couldn't be a { callback => $cb } hashref, just didn't see the need.

Hugo