duplicates:

• SR-6816 Let protocols inherit from class types

Issue Description:

This issue has two related manifestations - I believe it's a single bug (or two closely related)

Consider playground like this (working)

class SomeClass {
}

protocol Foo: class { // <-- this line 4 affects everything
    var isFooable: Bool { get set }
}


class ConcreteClass: SomeClass, Foo {
    var isFooable: Bool = false
}

let instance: SomeClass = ConcreteClass()

if let foo = instance as? Foo {
    foo.isFooable = false
    foo.isFooable
}

1) now if we change line 4 to

protocol Foo where Self: SomeClass {

we get an error at line

foo.isFooable = false

claiming foo is a let constant though I believe AnyObject reference behavior should be inferred

2) if we now change the condition to

if var foo = instance as? Foo {

we get EXC_BAD_EXEC at the line where we read the value (surprisingly not where we assign it)

3) we change protocol declaration to

protocol Foo: class where Self: SomeClass {

now all is working but we get two warnings

• first for the protocol declaration saying that Self: Any Class is redundant (but see 1) - it did not work if was not present

• second we don not have to declare foo as var in the conditional binding, what makes sense and can be easily fixed indeed