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Peter Shaw
Peter Shaw

Reputation: 1907

If not let - in Swift

is there is a way to negate the "if let" in swift? This looks silly to me:

    if let type = json.type  {

    } else {
        XCTFail("There is no type in the root element")
    }

I can't use XCTAssertNotNil, because json.type is a enum.

enum JSONDataTypes {
    case Object
    case Array
    case Number
    case String
}

Thanks a lot

EDIT: it is a:

var type: JSONDataTypes? = nil

Upvotes: 53

Views: 21878

Answers (3)

rickster
rickster

Reputation: 126167

Swift 2.0 (Xcode 7) and later have the new guard statement, which sort of works like an "if not let" -- you can conditionally bind a variable in the remainder of the enclosing scope, keeping the "good path" in your code the least-indented.

guard let type = json.type else {
    XCTFail("There is no type in the root element")
}
// do something with `type` here

The catch to this is that the else clause of a guard must exit that scope (because otherwise you'd fall into code after that clause, where the guarded variables, like type above, are unbound). So it has to end with something like return, break, continue or a function that is known to the compiler to never return (i.e. annotated @noreturn, like abort()... I don't recall offhand if that includes XCTFail, but it should (file a bug if it's not).

For details, see Early Exit in The Swift Programming Language.

As for really-old stuff... There's no negated form of if-let in Swift 1.x. But since you're working with XCTest anyway, you can just make testing the optional part of an assertion expression:

XCTAssert(json.type != nil, "There is no type in the root element")

Upvotes: 45

Can
Can

Reputation: 8571

Another alternative I've used a few times:

switch json.type
{
    case .None: // ...
    case .Some(.Object): // ...
    case .Some(.Array):  // ...
    case .Some(.Number): // ...
    case .Some(.String): // ...
}

Since the ? is actually Optional<T> which is an enum on its own, defined as:

enum Optional<T> : Reflectable, NilLiteralConvertible 
{
    case None
    case Some(T)

    ...
}

Upvotes: 2

Abhi Beckert
Abhi Beckert

Reputation: 33369

Here's how you do it:

if json.type == nil {
  // fail
}

Upvotes: 24

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