C unions in Xcode 7.1

Question

Created Oct ’15

Replies 4

Boosts 0

Participants 3

I wanted to play with unions imported from C in Xcode 7.1 beta 2, but can't get it to work. This is what the relase notes say:

"Field getters and setters are now created for named unions imported from C. In addition, an initializer with a named parameter for the field is provided. (19660119)"

And here's what I did:

Create a OS X command line project in Xcode 7.1.
Create a new C file and add it to the project. Say yes when Xcode asks you to create a bridging header.
Add the following code to the C header (taken from the release notes):

typedef union IntOrFloat {
   int intField;
   float floatField;
} IntOrFloat;

Include the C header in the bridging header.
In main.swift, try to create a variable of the union type:

let x = IntOrFloat(intField: 10) // error: Extra argment 'intField' in call

According to the release notes, this should work, but it doesn't. If I look at the interface Swift generated for the C header, I get this:

public struct IntOrFloat {
    public init()
}

But it should look like this:

struct IntOrFloat {
   var intField: Int { get set }
   init(intField: Int)

   var floatField: Float { get set }
   init(floatField: Float)
}

I can use the union normally in C code and call that C code from Swift, so I'm not sure what I'm doing wrong. Is this not fully functional yet in beta 2?

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Answer 1

OOPer OP

Oct ’15

Accepted Answer

Tested on Version 7.1 beta (7B75).

let x = IntOrFloat(intField: 10)
print(x.floatField) //->1.4013e-44

Generated Interface:

public struct IntOrFloat {
    public var intField: Int32
    public var floatField: Float
    public init(intField: Int32)
    public init(floatField: Float)
    public init()
}

I'm afraid you have mistakenly invoked another version of Xcode.

0

Answer 2

Jens OP

Oct ’15

Just wanted to add a related question: Will the memory layout and size (in Swift) be the same as those of the C union?

0

Answer 3

ole OP

Oct ’15

I'm afraid you're right. I was so sure I had updated to beta 2 on this machine but apparently I hadn't. Sorry for that and thanks for trying this out for me.

0

Answer 4

OOPer OP

Oct ’15

Unable to confirm with all possible cases, but it's working with this simple case:

var x = IntOrFloat(intField: 10)
print(x.floatField) //->1.4013e-44
print(sizeofValue(x)) //->4
x.floatField = 1.0
print(String(x.intField, radix: 16)) //->3f800000 = 1.0 in IEEE 754 float(binary 32)

0