relates to:

• SR-2790 Reject UnsafePointer initialization via implicit pointer conversion.

Issue Description:

The following observation was made today on Stack Overflow:

struct S {
    var prop : Int {
        didSet {
            print("did set!")
        }
    }
}
var s = S(prop:0)
let ptr = UnsafeMutablePointer(&s.prop)
ptr.pointee = 10
print(s.prop) // 0

This was said to be odd because things behave "as expected" if there is no setter observer on `prop`.

My response was to suggest that the way to get the expected result was to write:

struct S {
    var prop : Int {
        didSet {
            print("did set!")
        }
    }
}
var s = S(prop:0)
withUnsafeMutablePointer(to: &s.prop) { ptr in
    ptr.pointee = 10
}
print(s.prop) // 10

I also opined that the expression `UnsafeMutablePointer(&s.prop)` should never have compiled in the first place (I can't imagine which initializer the compiler imagines this would be), and that this, not the behavior when setting through the pointer's `pointee`, was the actual surprise.

However, I'm out of my depth.