Consider options for more specific ErrorTypes from saveContextAndWait() about coredatastack HOT 4 CLOSED

@lyricsboy You should be able to do the following

do {
    moc.saveContextAndWait()
} catch let error {
    let freeCast = error as NSError
    // do stuff with expected NSError
}

I believe this is what I ran into and @zwaldowski showed me this.

from coredatastack.

I have no idea why that works, but it does compile. I see this quote in the Swift guide:

“The cases of a switch statement use the forced version of the type cast operator (as, not as?) to check and cast to a specific type. This check is always safe within the context of a switch case statement.”

Excerpt From: Apple Inc. “The Swift Programming Language (Swift 2 Prerelease).” iBooks. https://itun.es/us/k5SW7.l

Is that what's going on? What does it mean to be "safe" in this context?

from coredatastack.

That's in general how switch statements work, it's the syntax within a switch statement. The let binding in switch cases uses as, which sounds pretty close to what you're quoting from the book, and doesn't use as? or as unless it's in a where clause. as compiles down to to the appropriate optimized as? when used within pattern matching.

ErrorType also comes at this/complicates this with a fair amount of magic. All types conforming to ErrorTypes are implicitly convertible to NSError to cross the Objective-C bridge, and therefore "safe". This allows you to throw from Swift and catch/handle it in Objective-C.

from coredatastack.

Ah, great explanation. Thanks guys. I think the ErrorType<->NSError magic is what I was missing.

from coredatastack.