On Jul 25, 11:10 pm, Petr Gladkikh <petrg...@gmail.com> wrote:
> I am trying to construct java object and assign it's fields from a map.
> That is given Java object of class Something { long id; String name; }
> and Clojure map {:id 12, :name "Impostor"}
> I would like to set fields of java object to respective values from map.
>
> Now, this works
> (let [o (Something.)]
> (set! (. o :id) 12)
> (set! (. o :name) "Impostor")
> o)
>
> But as soon as I use some value to get field expression compiler
> starts complaining "Invalid assignment target".
> that is
> (let [o (Something.)
> ff :id]
> (set! (. o ff) 12)
> o)
> I do not understand why this problem occurs. Any variations that I
> tried to made it work do not do the trick.
> Including weird (or ridiculous) ones like (set! (. o (symbol (str ":"
> (name ff))) 12)
>
> I suspect that this has something to do with compiler that needs field
> names at compile time but Clojure could use reflection for this...
>
> Can anyone point to what is wrong here?
>
> By the way is there already some function that allows to set fields of
> an object from a map?
Clojure *could* use reflection to do this...unless your object had a
field named ff! It has to decide at compile time how to look up a
field, and at that time it doesn't know your object won't have a .ff
field, so it figures, sure, I'll set the ff field.
If you really want to do this (hint: you don't), you can manually deal
with the reflection that the compiler would generate, as Shantanu
outlines.
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