Andrew Barnert wrote:
> On Sep 22, 2019, at 02:08, Nutchanon Ninyawee m...@nutchanon.org wrote:
> > Link is a language feature that allows multiple
> > variable names to always refer to the same underlying object define in a
> > namespace.
> > For now, if the variable a link with b. I will denote as a >< b or link('a',
> > 'b')
> > a = 2
> > a >< alpha # link 'a' with 'alpha'
> > b = 3
> > print(balpha) # print 9
> > alpha = 3
> > print(ba) # print 27
> > How would this work? I can think of a few options, but they all either
> > badly slow
> down every variable use, don’t work with locals, or require >< to be handled
> at
> compile time. Do you have at least a sketch of how this works?
> Also, do you have a real-life use case? Usually when you want the equivalent
> of
> “variable references” in Python, you just stick the value in a list or an
> explicit
> namespace; why isn’t that sufficient here? Also, usually you’re doing it to
> share a
> reference with a function, not just using another name in the same namespace;
> why do you
> need actual references here but not in the more general and more
> often-desired case?
> And finally, a whole bunch of questions on behavior:
> What happens if you del a?
> Is there a syntax to unlink variables? It seems like you’d want that at least
> at the
> interactive REPL.
> Is there any way to discover whether two names are linked?
> If you link a >< b and then link b >< c, does
> that make a three-way link, or unlink a from b?
> If you link two locals and capture them both in a closure, are the closures a
> single
> cell, or two cells that reference captured names that happen to be linked?
> What if you link two names in a class body?
> What if it’s inside code passed to eval or exec with normal locals and
> globals? Or with
> a custom dict subclass or Mapping class for one or the other?
> Can you link arbitrary targets (e.g., self.a >< self.b, or even a ><
> b[10]), or just bare names?
> If you call globals(), do you get back some kind of dict-like object that
> knows about
> the links (and can be inspected), or something that looks like a plain-old
> dict but if you
> assign to its a you also change b, or something that looks like
> a plain-old dict but if you assign to its a you unlink it?
Q: Do you have at least a sketch of how this works?
A: I have no idea how to make this work in c/kernel level. I have no experience
in implementing the core language before.
Q: What happens if you `del a`?
A: `del a` would unbind all linked names.
Q: Is there a syntax to unlink variables? It seems like you’d want that at
least at the
interactive REPL.
Q: Is there any way to discover whether two names are linked?
A: Yes, there is. It is currently open for design and discussion.
Q: If you link `a >< b` and then link `b >< c`, does
that make a three-way link, or unlink a from b?
A: That makes a three-way link.
Q: If you link two locals and capture them both in a closure, are the closures
a single cell, or two cells that reference captured names that happen to be
linked?
Q: What if you link two names in a class body?
Q: What if it’s inside code passed to eval or exec with normal locals and
globals? Or with a custom dict subclass or Mapping class for one or the other?
A: I don't understand the "single cell, or two cells" concept. I bet it relates
to inner representation like
[this](http://code.activestate.com/recipes/439096-get-the-value-of-a-cell-from-a-closure/).
I don’t know much about the implementation.
Q: Can you link arbitrary targets (e.g., self.a >< self.b, or even a ><b[10]),
or just bare names?
A: I would like to limit this to bare names at first for the sake of
simplification.
Q: If you call `globals()`, do you get back some kind of dict-like object that
knows about
the links (and can be inspected), or something that looks like a plain-old dict
but if you
assign to its `a` you also change `b`, or something that looks like
a plain-old dict but if you assign to its `a` you unlink it?
A: I thinks there should be a `links()` function to inspect linked variables.
globals() should behave like a plain-old dict but if you
assign to its `a` you also change `b`.
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