But for a struct to be immutable, you don't need all its properties to be let.
(I guess that's Derrick's point)
´´´
struct Person { /* . . . var properties . . . */ }
let john = Person() // john is completely immutable
´´´
If a struct has var properties, you can do a mutable copy, change it, assign it
to a new let, and you take advantage of immutability again.
´´´
let jim = { var copy = john
copy.firstname = "Jim"
return copy
}()
func with<T>(_ original: T, transform: (inout T) -> ()) -> T {
var copy = original
transform(©)
return copy
}
let jane = with(john) { $0.firstname = "Jane" }
// jane is also immutable
´´´
(I didn't check this compiles)
Pierre
> Le 19 déc. 2016 à 23:08, Andy Chou via swift-evolution
> <[email protected]> a écrit :
>
> Value semantics help reduce the issues around mutability, but they don't go
> away completely. I would like to create structs that are completely immutable
> after construction. Turning the properties into vars unfortunately loses this
> idea.
>
> The proposed 'with' function doesn't construct new instances, which means the
> let constants are already set. Nick's solution works, as it's basically a
> copy constructor that allows for changes while the new object is constructed.
> But it needs to be created for each struct. Which I'm fine with :)
>
> Andy
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
