Consider adding updateState convenience method

[jconst]

React provides the setState method which allows easily setting a subset, or all, of a component's state and triggering a render. Similarly, Few.swift provides the updateState function (but unfortunately does not make it easy to set just a piece of the state object). These functions, while simple, are valuable because they encourage a certain paradigm.

I personally use the following:

class Ref<T> {
  var value: T

  init(_ value: T) {
    self.value = value
  }
}

extension ComponentViewType {
  func updateState<T: ComponentStateType>(@noescape block: (Ref<T?>) -> ()) {
    let castedState = state as? T
    let reference = Ref(castedState)
    block(reference)
    state = reference.value
    renderComponent(CGSize.undefined)
  }
}

So then updateState can then be called like so:

struct BookState: ComponentStateType {
  var title: String
  var author: String
}

// then in a button callback or something:
updateState{ (state: Ref<BookState?>) in
  state.value!.title = "new title"
}

as opposed to currently needing to write:

var newState = myState!
newState.node = node
state = newState
renderComponent()

The (state: Ref<BookState?>) is necessary because the infra doesn't know what your ComponentStateType subclass is, but this can be solved if the state type is made a generic parameter of the view type, as Few.swift does.

If you think this seems reasonable I'd be happy to open a pull request! Interested to hear your thoughts.