Why don't structs have deinitializers in Swift like classes?

Question

I was just going through the Swift documentation of deinitializers and found that they only exist for classes. So I was just wondering why structs in Swift don't have deinitializers?

Please resd the comments on https://stackoverflow.com/questions/46842577/how-in-swift-to-know-that-struct-is-deleted-from-memory — Sulthan, May 17 '18 at 19:52
Supposing that structs did have deinitializers, what would you like to use them for? — Alexander, May 17 '18 at 20:07
`Deinitializers` are only available on `class` types as described in documentation. — Mannopson, May 18 '18 at 02:38

matt · Accepted Answer · 2018-05-18T15:31:40.063

29

deinit is for reference types (see https://stackoverflow.com/a/27366050/341994 for what that means) where the object pointed to persists independently until a reference count drops to zero.

A struct is a value type and does not require memory management that would need a deinit. Structs are not independently persistent the way classes are. Merely setting a property of a struct destroys it and replaces it. Assigning a struct copies it. Structs are created and destroyed in a highly lightweight way. They don’t need to signal their destruction; they are too lightweight for that.

edited May 18 '18 at 15:31

answered May 17 '18 at 19:56

matt

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So in struct we also don't need to use "weak var someStruct" ? – Asi Givati Nov 02 '20 at 13:37

Nitish · Answer 2 · 2018-05-17T19:51:03.393

Structs are deallocated when they go out of scope. You can't put a deinit in a struct, but here is a workaround. You can make a struct that has a reference to a class that prints something when deallocated.

class DeallocPrinter {
    deinit {
        print("deallocated")
    }
}

struct SomeStruct {
    let printer = DeallocPrinter()
}

So when the struct is deallocated - if you haven't made a copy of the struct, it'll print deallocated when it's deallocated, since the DeallocPrinter will be deallocated at the same time the struct is deallocated.
Also, structs do not really have instances in the sense that classes do (i.e. they don't have an identity), and there also aren't "references" to structs.

Your workaround cannot work. It wont print the message until the last copy od the struct goes out of scope. — Sulthan, May 17 '18 at 19:48

Why don't structs have deinitializers in Swift like classes?

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