Swift struct type recursion

Question

Why can't structs have recursive value types in Swift? Is this a temporary limit of the language or is it as intended?

I feel that the ability to declare a binary tree node as a struct with recursive types in it to be the most natural implementation.

struct TreeNode<E>{
var leftNode:TreeNode<E>
var rightNode:TreeNode<E>
var element:E
}

Answer 1

The answer is in your question: structs are value types. If you include a substruct B into a struct A, it means, that one object of type A will have a size sizeof(all_other_fields_of_A) + sizeof(B). So, a value type can not be recursive: it would have infinite size.