Xcode 16 Beta 3: "Cannot expand accessors on variable declared with 'let'"

Question

mark-ger OP

Created 3d

Replies 3

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Participants 2

Running into this new issue in beta 3.

All of our immutable model attributes are now triggering swift compiler error from the title (tied to swift 6 - warning in swift 5).

Neither warning or error show up on previous builds.

Anyone else running into this? Hopefully not a limitation on swiftData that attributes must be mutable?

filed as: FB14379932 (new in Xcode 16 beta3: "cannot expand accessors on variable declared with 'let'" in SwiftData Models)

Answered by DTS Engineer in 796071022

Yeah, this is a change introduced in beta 3. Every SwiftData attribute is converted (expanded) to a computed property with accessors via SwiftMacro, and since beta 3, the conversion requires the attribute be var.

I think you can go ahead to apply the change to your SwiftData attributes. Doing that shouldn't have any negative impact.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

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Answer 1

DTS Engineer OP

Apple

3d

Recommended

Yeah, this is a change introduced in beta 3. Every SwiftData attribute is converted (expanded) to a computed property with accessors via SwiftMacro, and since beta 3, the conversion requires the attribute be var.

I think you can go ahead to apply the change to your SwiftData attributes. Doing that shouldn't have any negative impact.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

1

Answer 2

mark-ger OP

3d

Thank you for confirming the change. Is this going to be a documented limitation of SwiftData?

It is useful to be able to express the immutability of particular model attributes. I can understand if SwiftData may now be unable to handle that immutability constraint, but that change seems like it should be a documented property of SwiftData and not just a compiler error.

If it isn't a SwiftData design decision but a limitation of macros I would encourage the restoration of the previously shipping behavior.

1

Answer 3

DTS Engineer OP

Apple

2d

Disallowing let for an attribute that is converted to a computed property is a Swift language feature, and so the change is intentional.

I agree though that there is a need to express immutability for a SwiftData model attribute, and so will encourage you to voice your opinion in your feedback report for the team to consider.

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

0