Swift Compilation Error for Property Wrappers with Codable in multiple files

Question

Compilation failed for property wrappers with codable in multiple files.

I found test codes in Swift source below:

• property_wrappers_codable_multifile_other.swift

@propertyWrapper
struct Printed<Value: Codable>: Codable {
    var wrappedValue: Value {
        didSet { print(wrappedValue) }
    }
}

struct Foo: Codable {
    @Printed var bar: Bool = false
}

• property_wrappers_codable_multifile.swift

func test(_ value: Foo = Foo()) {
  let _: Codable = value
}

and use them in my test project:

TestProject

But compilation failed with error:

Type 'Foo' does not conform to protocol 'Encodable'

How to fix it?

Answer 1

It is a question of visibility... the simplest fix is just to move those helper structs into ViewController module as below... run, and all works (tested with Xcode 11.2)

Answer 2

The test Foo struct is not necessary to be Codable.

The test is on the bar property. and a Bool type is already comformed to Codable.

struct Foo{
    @Printed var bar: Bool = false
}

func test(_ value: Foo = Foo()) {
   var m = value
   m.bar = true. // will call didSet in @printed struct
}

Answer 3

Allow test to accept a generic Codable if that is the only requirement for that function:

func test<T: Codable>(_ value: T) {
    let val = value
}