Open Radar

 
Summary:
See attached playground for minimal reproducing example.
Protocol P has a get-only variable declaration.
Another variable has type P and a set/didSet.
Whenever the variable from the protocol is accessed via the protocol-typed variable, setter and didSet for the latter variable are called.

Steps to Reproduce:
Open and run the attached playground in Xcode 7.
Notice that "didSet" is printed 42 times.

Expected Results:
didSet is expected to never be called

Actual Results:
didSet is called each time variable is accessed (42 times)

Version:
Xcode 7.0 (7A220)
OS X 10.10.5 (14F27)

Notes:
DidSet no longer gets unexpectedly called if the protocol P is restricted to AnyObject or—surprisingly—the variable "x" declaration in protocol is changed from {get} to {get set}.
I suspect that variable "x" getter is erroneously treated as a mutating function, in which case the setter invocation would be due.

Configuration:
Xcode 7 playground, iOS 9 simulator and iOS 9 devices

Attachment:

protocol P {
	var x: Bool { get }
}
class A: P {
	var x = true
}
var variable: P = A() {
	didSet {
		print("didSet")
	}
}
for _ in 1...42 {
	variable.x // prints "didSet"
}