Here’s a pattern I find myself doing quite often:
1> class Child {
2. var onSomeEvent: () -> Void = { }
3. }
4> class Parent {
5. let child = Child()
6. init() {
7. child.onSomeEvent = doSomething
8. }
9. func doSomething() {
10. }
11. }
I have some ownership hierarchy of classes (often controllers — view
controllers — views), where I pass information from children up to parents
using closures set by the parent.
I like this pattern because children classes don’t have to be tied to knowledge
about their parents, and I don’t have to define delegate protocols. It’s very
clean, and also very easy to set up.
The only problem is that there’s a strong danger of introducing reference
cycles.
With class properties, you can quite easily see the potential for a reference
cycle and mark references to parents with weak/unowned. And with `self`
captures in closures, you’re reminded of memory management by having to be
explicit about `self`. But when passing references from parents to children,
there’s no way to mark the closure property as `weak` (and there’s no reminder
of the danger).
* * *
Right now, every time I pass a closure down to children, I have to wrap my
references like so:
{ [unowned self] self.doSomething($0) }
instead of a neat and simple function reference:
doSomething
I think it would be useful to have a shortcut syntax for creating weak and
unowned references to functions, like so:
@unowned(doSomething)
or perhaps:
#unowned(self.doSomething)
* * *
An alternative would be the ability to mark closure properties as weak or
unowned. Then I could, at the *child* level, say:
unowned let onSomeEvent: () -> Void
* * *
Does this make sense? What do you think?
— Radek
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
