[Proposal] Defstruct could set read only properties

[Pedro Carvalho]

defstruct foo [

:a,

 property: b , fn  x -> a*2 end

] 

when foo[:b] is called  the function would be invoked by overriding the acess operator,
this way you can get more redability in your code than Foo.calculate_b(a) and simply overriding fetch on the module

[an.le...@gmail.com]

Hey Pedro,

In Elixir, data has no behavior associated with it. Data is just data. Functions are where the behavior is encapsulated. So, a feature like "dynamic access" fields like the one you propose would clash with this core idea. There are also some other issues:

• Having Foo.calculate_b(a) is also explicit and predictable, compared to having foo[:b] be dynamic.
• What if you had side-effects in the access function, like changing some state or writing to a file? Then, every call to foo[:b] would perform those side effects implicitly.
• The particular example you provided wouldn't work, since you can't reliably have function values at compile time (like the fn used there).

Thanks anyways for the proposal!

Andrea

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