Recursive Data Structures

[andrew batutin]

Hi

Swift is nice with all the functional goodies included int it.

But one thing really annoying for me. 

We can't define recursive data structures

So such code

public struct BinaryTree<T:Comparable>{

    var leftNode:BinaryTree? = nil

    var rightNode:BinaryTree? = nil

    var nodeValue:T? = nil

}

is not compilable cause of 

BinaryTree.swift:9:15: Recursive value type 'BinaryTree<T>' is not allowed

error

I've seen a way around this issue boxing the leaf value at new class. But it looks ugly.

Is there any better way?

Or can we make Apple improve compiler?

[andrew batutin]

Hi Andrew

You can just use class instead of struct

It's not perfect. But tolerable.

[andrew batutin]

And how about Empty type?

Is there smthng is Swift to represent Empty type?

Like empty leaf?

On Thursday, December 4, 2014 11:36:33 PM UTC+2, andrew batutin wrote:

[Jens Alfke]

On Dec 4, 2014, at 1:59 PM, andrew batutin <abat...@googlemail.com> wrote:

And how about Empty type?

Is there smthng is Swift to represent Empty type?

That's what the "?" syntax is for. It denotes a reference that may be empty.

—Jens

[Jeremy Pereira]

As I understand it, structs are value types. Trying to define a recursive struct, even using optionals is effectively defining an infinitely large object.

You wouldn't expect this to work in C would you:

struct BinaryTree
{
struct BinaryTree left;
struct BinaryTree right;
};

You need to use references, which means in Swift, you need to use a class not a struct.

class Foo<T: Comparable>
{
var left: Foo<T>?
var right: Foo<T>?
var value: T?

init(left: Foo<T>?, right: Foo<T>?, value: T?)
{
self.left = left
self.right = right
self.value = value

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