Hello,
I have some ID types that are simple ints coming back from a database. I
wanted to improve type safety so I don’t accidentally assign product IDs to
user IDs, etc. I want to be able to print it and use it as a dictionary key.
So it is a trivial wrapper of Int. E.g.
struct CustomerID: Hashable, CustomStringConvertible {
init(_ value: Int) { self.value = value }
let value: Int
var hashValue: Int { return value.hashValue }
var description: String { return String(value) }
}
func ==(lhs: CustomerID, rhs: CustomerID) -> Bool {
return lhs.value == rhs.value
}
While it isn’t too much code, it seems like a lot boilerplate. I tried to
reduce the boilerplate with protocol extensions. After a little bit of
compiler fighting I came up with:
public protocol IDType: Hashable, CustomStringConvertible {
init(_ value: Int)
var value: Int { get }
}
extension IDType {
public var hashValue: Int { return value.hashValue }
public var description: String { return String(value) }
}
Notes (1) compiler made me declare my protocol public since Hashable and
CustomStringConvertible are public. (2) I could not implement init(_ value:
Int) in the extension so I have to do that each time (3) Self requirement built
into Hashable meant that I could not implement an == for all IDTypes. So the
final product looks like the following. Given the additional complexity,
doesn’t seem like it is worth it.
public struct ProductID: IDType {
public init(_ value: Int) { self.value = value }
public let value: Int
}
public func ==(lhs: ProductID, rhs: ProductID) -> Bool {
return lhs.value == rhs.value
}
I wonder if the hive mind had any better ideas or different approaches for
creating such types with minimal boilerplate. [Is there a possible new
language feature coming that will make this more trivial?]
Ray
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