Re: sunday afternoon whishlist

[steve donovan <steve.j.donovan@...>]

2010/5/9 Tony Finch <dot@dotat.at>:
> Perl's handling of nonexistent indices is more complicated than that.
> If you write $x->{y}->{z} (Perl for x.y.z) then $x-{y} is autovivified
> into a reference to a hash. This also applies to array references.

Autovivification also solves the inverse problem, when you are writing
things like t.a.b.c = 'value';  it would create the intermediate
tables if they didn't exist already.

Setting the metatable for nil is a cute hack but like all global
metatable hacks it affects everything, which is ok for small-ish
systems where you control everything.

BTW, there is a little inconsistency; tables do not have a default
metatable.  If this were so, then another category of cute global
hacks becomes possible. ;)

While we're talking about wishlists, it would be useful if there were
a __methindex metamethod as well as __index, so that the lookup in
obj:name() does not have to be the same as obj.name/obj['name']. (This
is not a new suggestion, but IHMO a useful one to keep foregrounded.)
The obvious gain is able to define a Map class where you don't get
false positives (i.e. map['update'] is always true if there is a
Map.update method) but it's also useful for a List class: one can then
efficiently implement ls[-1] like Python without having to catch
everything using __index.

steve d.