Using Memoize is certainly possible, but you'll need to jump through a couple of hoops - you must only memoize() the 'get' functionality, and need to be able to clear the cached value as part of 'set' - so it's probably easiest doing it the way you already are.

I've not used this myself, but I believe it should work something like this (untested):

  use Memoize;
  my(%_getscalar, %_getlist);
  memoize(__PACKAGE__ . '::_get',
    SCALAR_CACHE => [ HASH => \%_getscalar ],
    LIST_CACHE => [ HASH => \%_getlist ],
  );

  # in _set()
  sub _set {
    my($self, $element, $value) = @_;
    ...
    # default normaliser
    my $cachekey = join "\034", $self, $element;
    delete $_getscalar{$cachekey};
    delete $_getlist{$cachekey};
    ...
  }
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