Wrapped property with #propertyWrapper won't return wrapped type - swift5

Question

In this simplified example, I make a propertyWrapper of an UInt to hold a Natural Number (an Integer > 0). My own example uses a more complex filter but this shows the issue. Rather than find a workaround, the point of the question is to shed light on the confusing (to me) error.
Assigning it to a simple UInt brings the error message listed.
Using its wrappedValue property as in the following line works fine. But surely the whole point of the wrapping is to be able to treat it as an UInt as returned by the get?
The error "cannot assign value of type 'NonZero' to type 'UInt" appears to undermine the whole point of the wrapper type. What am I misunderstanding?
Xcode 11.0
import Foundation
#propertyWrapper
struct NonZero {
private let myNumber : UInt
init(n : UInt)
{
if ( n == 0){fatalError(" cannot be 0")}
myNumber = n
}
var wrappedValue: UInt {
get { return myNumber }
}
}
struct Nums {
var num :UInt
init( nz: NonZero){
num = nz //error message "cannot assign value of type 'NonZero' to type 'UInt"
num = nz.wrappedValue //no error
}
}

Answer 1

This is not how property wrappers work. The code:
init(nz: NonZero)
declares nz to have the type NonZero – which is just the struct defined earlier, NonZero here is not being used as a wrapped property.
A wrapped property is used as an attribute on a property declaration, for example:
#NonZero var num : UInt = 1
[Putting that in the code requires changing the parameter label of NonZero's init to be changed to wrappedValue, e.g.:
init(wrappedValue : Uint) { ... wrappedValue ... }
]
You could write the init of struct Nums as:
init(nz: UInt)
{
num = nz // ok *after* you add a `set` to `NonZero`, will `fatalError` if `nz` is zero
let unwrapped : UInt = num // ok
print(unwrapped) // so you see it worked
}
Keep exploring! You might find SE-0259 Property Wrappers (Apple) and Swift Property Wrappers (NSHipster) useful.
HTH