What is a 'variable initialization expression'?

[Nevin]

I’d just like to reference the acceptance notes for SE–0242:

@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.