MaybeEquatable.swift

// see also https://gist.github.com/tarunon/85bdeccf8bc8f44b7b27d4974e0a843f

public protocol MaybeEquatable {
    func _isEqual(to other: Any) -> Bool
    func __isEqual(to other: Any) -> Bool
}

extension MaybeEquatable {
    public func __isEqual(to other: Any) -> Bool {
        return false
    }
}

extension MaybeEquatable where Self: Equatable {
    public func __isEqual(to other: Any) -> Bool {
        guard let other = other as? Self else { return false }
        return self == other
    }
}

extension MaybeEquatable {
    public func _isEqual(to other: Any) -> Bool {
        // you can use dynamic conditional dispatch here
        __isEqual(to: other)
    }
}

// end user interface
func anyIsEqual(_ a: Any, _ b: Any) -> Bool {
    guard let a = a as? MaybeEquatable else { return false }
    return a._isEqual(to: b)
}

// you need to mark your type
extension String: MaybeEquatable {}

print(anyIsEqual("str", "str")) // => true
print(anyIsEqual({}, {})) // => false