How to dynamically track changes to an `Association`

Question

Bug introduced in 10.4 or earlier and persisting through 11.1.1

CASE:3892974

Thanks for bringing this to our attention. A report has been filed with the developers.

I can track changes to a list with Dynamic without too much difficulty

foolist = {};
Dynamic[foolist]

And if I were to append an element to foolist, the dynamic expression will refresh to {list}

AppendTo[foolist, list]

But when I do the same with an association,

foobar = <||>;
Dynamic[foobar]

And add a new entry to it

AssociateTo[foobar, foo->bar]

The dynamic expression won't be able to capture the change. Am I doing something wrong?

I don't think you do anything wrong, unless I'm missing something I think you should report this. p.s. notice that you can still do AppendTo[foobar, foo -> bar] and it will work well. — Kuba, May 18, 2017 at 18:40
@Kuba Ah thanks! And it seems that all Set assignments to an association can be tracked as well — arax, May 18, 2017 at 20:50
Indeed. I've reported that, will let you know in case of any news. (CASE:3892974) — Kuba, May 18, 2017 at 21:38

Kuba · Accepted Answer · 2017-05-23 19:38:20Z

1

Meanwhile you can use:

AppendTo[foobar, foo->bar]

or more functional style:

foobar = <|foobar, foo->bar|>;

foobar = Append[foobar, foo->bar];

answered May 20, 2017 at 11:22

Kuba♦

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$\begingroup$ Won't the result of the "more idiomatic" be an undesirable <|<||>, foo->bar|>? $\endgroup$
– LLlAMnYP
May 20, 2017 at 15:27
$\begingroup$ @LLlAMnYP I don't understand, have you tried? But maybe I shoud've said "more functional style". $\endgroup$
– Kuba ♦
May 20, 2017 at 16:40
$\begingroup$ since it's the weekend, no, I haven't. Are you saying, the first element won't be the empty association that foobar was before assignment? Since for, say, a list saying foobar={}; foobar={foobar, foo->bar} will give {{}, foo->bar} and not {foo->bar} $\endgroup$
– LLlAMnYP
May 21, 2017 at 17:03
$\begingroup$ @LLlAMnYP <|assoc1, assoc2|> works like Merge[{assoc1, assoc2}, Last] $\endgroup$
– Kuba ♦
May 21, 2017 at 17:36
$\begingroup$ Interesting, so it autoflattens. $\endgroup$
– LLlAMnYP
May 21, 2017 at 17:37

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