How to call UIApplicationMain in main.swift in Swift 3

Question

I don't understand how to write a main.swift file in Swift 3 (current toolchain). We used to write it like this:

UIApplicationMain(
    Process.argc, Process.unsafeArgv, nil, NSStringFromClass(AppDelegate)
)

But now that won't compile, because there is a type mismatch between

Process.argv

, which is typed like this:

UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>

and the second parameter to UIApplicationMain, which is typed like this:

UnsafeMutablePointer<UnsafeMutablePointer<Int8>>!

As you can see, they are subtly different. I am able to work around the problem by writing this:

withUnsafeMutablePointer(&Process.unsafeArgv.pointee!) {
    UIApplicationMain(
        Process.argc, $0, nil, NSStringFromClass(AppDelegate)
    )
}

But whether that is safe or correct, I have no idea.

Swift

13k

Posted by

mattn

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Answer 1

This seems like fallout from the recent change in how unsafe pointers interact with optional. I think

Process.argv

is correct, in that

Process.argv

itself can’t be nil, but any of the elements it points to can be nil. I recommend that you file a bug against

UIApplicationMain

. Please post your bug number, just for the record.

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Posted by

eskimo

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Answer 2

Thanks, radar 26062787 submitted. I'm also going to post this on bugs.swift, as it affects them. They had `@UIApplicationMain` wrong on the last toolchain release, and if the signature of UIApplicationMain changes again, `@UIApplicationMain` will be wrong again.

Posted by

mattn

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Answer 3

Jordan Rose has suggested working around it like this:

UIApplicationMain(
    Process.argc, UnsafeMutablePointer<UnsafeMutablePointer<CChar>>(Process.unsafeArgv), nil, NSStringFromClass(AppDelegate)
)

Posted by

mattn

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Answer 4

This broke for me in Xcode 8 beta 6. What is the new suggestion?

Posted by

ellucian-jkh

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Answer 5

Like this:

UIApplicationMain(
    CommandLine.argc,
    UnsafeMutableRawPointer(CommandLine.unsafeArgv)
        .bindMemory(
            to: UnsafeMutablePointer<Int8>.self,
            capacity: Int(CommandLine.argc)),
    nil,
    NSStringFromClass(AppDelegate.self)
)

Posted by

mattn

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How to call UIApplicationMain in main.swift in Swift 3

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