ios - Swift (beta 3) "NSDictionary? does not conform to protocol 'Equatable'"

Question

I've had a fair few warnings and errors in my Swift code since updating to the latest Xcode 6 DP3. Most have been resolved by adopting the newly changed syntax however there is one error which seems strange.

The following code gives the error Type 'NSDictionary?' does not conform to protocol 'Equatable':

if (launchOptions != nil && launchOptions![UIApplicationLaunchOptionsRemoteNotificationKey] != nil) {

Does anyone have a solution? I'm probably overlooking something simple here..!

Thanks

Answer 1

There is a regression in Beta 3 causing that Optional<T> cannot be compared with nil if T is not Equatable or Comparable.

It's a bug caused by the removal of the _Nil type for which the equality operators were defined. nil is now a literal. The bug has been confirmed by Chris Lattner on Apple Dev Forums

Some workarounds:

You can still use .getLogicValue()

if launchOptions.getLogicValue() && ... {

or directly

if launchOptions && ... { //calls .getLogicValue()

or you can use the "Javascript object to boolean" solution

var bool = !!launchOptions

(first ! calls the getLogicValue and negates, the second ! negates again)

or, you can define those equality operators by yourself until they fix it:

//this is just a handy struct that will accept a nil literal
struct FixNil : NilLiteralConvertible {
    static func convertFromNilLiteral() -> FixNil {
        return FixNil()
    }
}

//define all equality combinations
func == <T>(lhs: Optional<T>, rhs: FixNil) -> Bool {
    return !lhs.getLogicValue()
}

func != <T>(lhs: Optional<T>, rhs: FixNil) -> Bool {
    return lhs.getLogicValue()
}

func == <T>(lhs: FixNil, rhs: Optional<T>) -> Bool {
    return !rhs.getLogicValue()
}

func != <T>(lhs: FixNil, rhs: Optional<T>) -> Bool {
    return rhs.getLogicValue()
}

Example:

class A {
}

var x: A? = nil

if x == nil {
    println("It's nil!")
}
else {
    println("It's not nil!")
}

However, this workaround might cause other subtle problems (it probably works similarily to the _Nil type in Beta 2 which was removed because it was causing problems...).