Properties with default values are always initialized before the body of any init(), even for Decodable.init — why is this?

[1-877-547-7272]

I think this is definitely worth addressing — it's caused a lot of performance problems and general confusion over the years.

The Core Team considers this behavior a bug.

@tkremenek

The proposal review also discussed an interesting behavioral quirk with initial values and side-effects, for example:

struct Foo {
  var i: Int = getDefaultValue()
}

struct Bar {
  var i: Int = getDefaultValue()
  init(i: Int) { self.i = I }
}

let x = Foo(i: 1)  // No side effects
let y = Bar(i: 1)  // Yes side effects

The Core Team felt that this was a bug in the compiler's implementation of initializers. The failure here is that Bar calls the side effect, and it is not the right behavior. Addressing this would likely require an evolution proposal, or at least an assessment of whether or not fixing this would break existing code.