CODEWITHSUNDEEP
ocamlmutablerecords
nathan
nathan

Reputation: 1119

ocaml - array of record with mutable field

I'm new to OCaml and i'm trying to understand the concept of mutable record field.

I'd like to create an array of records and that record contains a boolean mutable field. So i did something like:

type t = {i: int; mutable b: bool};;

I want to be able to change the value of the 'b' field of the record, so i put it mutable

let m = Array.make 10 ({i = 5; b = false});;

Here i try to set the b field of the record located at the first index of my array :

(Array.get m 0).b <- true;;

The problem is want i do it, it will set 'b' field of all the records of the array, and this is not what i want.

Does the mutable fields of a same record share the same memory emplacement? How can i do to change the value of the 'b' field of a specific record?

Upvotes: 1

Views: 643

Answers (1)

cygin
cygin

Reputation: 373

As the documentation states, Array.make creates an array whose elements are all physically equal. That's not a problem if these elements are immutable, but as you saw, you have to take that into account if they are mutable.

What you can do is use Array.init, to create a different object for every cell of your array:

let m = Array.init 10 (fun _ -> {i = 5; b = false});;

Upvotes: 7

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