Making nested arrays of arbitrary depth conform to protocol of its innermost Element

Using Swift
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1

Hi,
let's say I have a protocol MyProtocol and a class MyClass: MyProtocol conforming to MyProtocol.

How can I declare nested arrays of arbitrary depth of MyClass to all conform to MyProtocol? So how can I make arrays of type[MyClass], [[MyClass]], [[[MyClass]]], ... conform to MyProtocol?

An example where I see this implemented is for the Codable Protocol, as long as MyClass: Codable conforms to Codable, [MyClass].self is Codable.Type returns true, so does [[MyClass]].self is Codable.Type and so forth. This is exactly the behavior I would like to have for MyProtocol.

Making this work for [MyClass] is simple:
extension Array: MyProtocol where Element: MyClass { }

But how do I declare this for nested arrays of MyClass with arbitrary depth?

2

Your extension is nearly correct. What you want is Element: MyProtocol:

protocol MyProtocol {}

extension Array: MyProtocol where Element: MyProtocol {}

struct Foo: MyProtocol {}

[Foo()] as MyProtocol
[[Foo()]] as MyProtocol
[[[Foo()]]] as MyProtocol
[[[[Foo()]]]] as MyProtocol
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3

Thank you very much. It's actually kind of embarrassing I did not think of that kind of recursion.

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