So \ refers to the immediately-precedent object. In the example below, \ refers to people.
Sort of.
The method signature of this particular version of ForEach looks like this:
init(
_ data: Data,
id: KeyPath<Data.Element, ID>,
@ViewBuilder content: @escaping (Data.Element) -> Content
)
We can see from the notes on this page that the data parameter has to be something that conforms to the RandomAccessCollection protocol (like, say, an array). RandomAccessCollection has a generic type parameter called Element that refers to the type of whatever is contained in the collection.
You can see from the above method signature that id is a key path pointing to a property on the type Data.Element that is generically labelled ID.
So the \ doesn't refer to the immediately-precedent object, which is a collection of some things. It refers to the some thing that is contained in the collection.
To use our example again, let's presume we have a struct called Person that has a property fullName by which every person can be uniquely identified (nevermind that this would actually be a terrible way of doing it):
struct Person {
let firstName: String
let lastName: String
var fullName: String {
"\(firstName) \(lastName)"
}
}
And we have a collection of Person items that we store in an array called people:
let people = [Person]()
And we want to loop through people and display each Person in a neat list or something:
ForEach(people, id: \.fullName) { person in
//blah blah blah display stuff
}
What this tells us (looking back up at our method signature) is that our Data type is [Person], an array being something that conforms to the RandomAccessCollection protocol. Which means that Data.Element (the type of thing contained in Data) is Person and the key path supplied to the id parameter is a KeyPath<Person, fullName>, meaning "take a Person object and refer to its fullName property".
So to rephrase your initial statement:
\ refers to the type of the items in the immediately-precedent collection. In the example below,\ refers to Person.
