I want to define a property for a struct/class that is nil after
initialization, but later is guaranteed to have a value after I manually assign
to it. I think implicitly unwrapped optional property is designed specifically
for that.
However, the problem arises when it comes to how do I enforce that I never
mistakenly assign nil to this property?
struct Foo {
var name: String!
}
var foo = Foo()
I can do foo.name = nil and it will compile just fine.
I guess I could do a run-time check with something like:
struct Foo {
var name: String! {
willSet {
if newValue == nil {
fatalError("nil isn't allowed")
}
}
}
}
But it feels ugly, and seems to be something checkable at compile time.
I could define a new setter method:
struct Foo {
private(set) var name: String!
mutating func setName(_ name: String) {
self.name = name
}
}
But it feel tedious. Enforcing non-nil assignment probably fits 90% of the use
cases of IUOs, since that’s basically their definition. Having to deviate from
direct assignment syntax in usage and also define a new setter method for the
majority cases seems unfortunate.
I wonder if it’s desirable to define an attribute or something to ask the
compiler to only allow non-optionals to be assigned to IUO properties?
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