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It is possible to implement OOP in Mathematica using something like

obj=c[<|a->1,b->2|>]

and it's convenient to extract value from the object by setting:

c[a_][b_]:=a[b]
obj[a]

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but how to write a convenient value assignment so that this form of set action is valid?

obj[a]=3

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obj

c[<|a->3,b->2|>]

Thanks!

My (obviously unsuccessful) attempts:

c /: Set[o : (c[a_])[b_], val_] := (o=c[ReplacePart[a,Key[b]->val]])

This obviously won't work as the HoldFirst attribute of Set prevent the pattern matching of c[a_]

but without it:

Set[o_[b_], val_]/;Head[o]==c := (o=c[ReplacePart[a,Key[b]->val]])

Set is Protected and simply matching all o_[b_] type and then filter by Head is simply so inefficient.

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    $\begingroup$ You have to use Language`SetMutationHandler. See here for detailed info an an example. $\endgroup$
    – Henrik Schumacher
    Jun 15, 2018 at 6:46
  • $\begingroup$ @HenrikSchumacher Thanks! I will have a look! $\endgroup$
    – Wjx
    Jun 16, 2018 at 4:14
  • $\begingroup$ Please try to determine the place of your approach among the ones listed (and taxonomized) here: "Which Object-oriented paradigm approach to use in Mathematica?". Consider posting an answer (in the referred MSE discussion.) $\endgroup$
    – Anton Antonov
    Dec 25, 2021 at 14:05

1 Answer 1

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Kernel definitions precede over user definitions, and subvalues precede over upvalues. As @HenrikSchumacher commented, Language`SetMutationHandler should be used.

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