In my first real code using Moose, I noticed some things about attributes.

Basically, it is not nice to have to call functions to get and to set each time. I noticed later that some use of "native traits" delegation can mitigate that, but not completely, as it would lead to a proliferation of specific methods; but that's an issue really because Perl built-in types like arrays are not themselves accessed via method syntax and built-in functions don't take references.

The real issue, that can't be put off on other things still needing to catch up, concern very simple types like plain numbers and strings.

Consider:

my $linenum= $self->input_line_number;
++$linenum;
$self->input_line_number ($linenum);

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Or perhaps$self->input_line_number(1+$self->input_line_number);. But, recall that the ++ syntax is beloved by millions and for a reason! It is quite a bit out of the way to not be able to manipulate things in-place.

Now in Perl6, the accessors return lvalues, so something like ++$self->input_line_number would work just fine.

So here is a specific question: why not have an lvalue accessor in Moose? That could be enabled on request, or the default when it is declared to be a non-reference type.

More generally, how are people coping with the large affordance distance between the method's code and the per-class instance data? It's always been large in Perl 5, but at least I could refer to the slots (via hash access) as lvalues. It seems to be a chore, all the time, for code to get to its values. In C++ you just say x in scope; in Moose you have to say $self->x twice, to get and again to set, and work on a copy.

In reply to Some thoughts on Moose Attributes by John M. Dlugosz

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