[swift-users] Reducing the boilerplate for my ID types

[Ray Fix]

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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