Before I respond to a specific point below, I'd like to make a general observation.
I changed the subject line of this sub-thread to discuss a feature of Julia, which allows one to write vectorized code in standard infix arithmetic notation, that applies to any array type, using any existing function or operator, WITHOUT having to wrap your data in a special delegate class like this "Vector".
So as far as I'm concerned, this entire discussion about this wrapper class misses the point.
(Aside: why is this class called "Vector" when it doesn't implement a vector?)
Anyway, on to my response to a specific point:
On Mon, Feb 04, 2019 at 11:12:08AM -0500, David Mertz wrote:
On Mon, Feb 4, 2019 at 7:14 AM Kirill Balunov email@example.com wrote:
len(v) # -> 12
v[len] # -> <Vector of [3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3]>
In this case you can apply any function, even custom_linked_list from my_inhouse_module.py.
I think I really like this idea. Maybe as an extra spelling but still allow .apply() to do the same thing. It feels reasonably intuitive to me. Not *identical to* indexing in NumPy and Pandas, but sort of in the same spirit as predicative or selection based indices.
What do other people on this thread think? Would you learn that easily?
obj[len] already has an established meaning as obj.__getitem__(len). There's going to be clash here between key lookup and applying a function:
obj[len] # look up key=len obj[len] # apply function len
Mathematica does use square brackets for calling functions, but it uses ordinary arithmetic order len[obj] rather than postfix order obj[len].
At the risk of causing confusion^1, we could have a "vector call" syntax:
# apply len to each element of obj, instead of obj itself len[obj]
which has the advantage that it only requires that we give functions a __getitem__ method, rather than adding new syntax. But it has the disadvantage that it doesn't generalise to operators, without which I don't think this is worth bothering with.
^1 Cue a thousand Stackoverflow posts asking whether they should use round brackets or square when calling a function, and why they get weird error messages sometimes and not other times.