Hello,

I was wondering if OpenAPI or the OpenAPI generator could define new scalar types.

New scalar types help disambiguating scalar values such as integers or strings by making them strongly typed: this is a user id, this is an ISO-8601 date, this is a number of seconds, this is an amount of cents. With strong typing, mixing apples and oranges is impossible.

OpenAPI has something that looks pretty much like this:

components: schemas: # A custom string scalar: URL: type: string PhoneNumber: type: object properties: localized_description: type: string # Not a string, but a URL: url: $ref: '#/components/schemas/URL' required: - localized_description - url

But OpenAPI Generator imports them as their raw Swift type. For example:

// Generated public enum Components { public enum Schemas { /// - Remark: Generated from `#/components/schemas/URL`. public typealias URL = Swift.String } }

Somehow I was expecting Components.Schemas.URL to be generated as a RawRepresentable type, as below. I thought that the definition of #/components/schemas/URL was a sufficient hint for the desire of a custom type:

// My expectation public enum Components { public enum Schemas { /// - Remark: Generated from `#/components/schemas/URL`. public struct URL: Codable, Hashable, Sendable, RawRepresentable { public var rawValue: String public init(rawValue: String) { self.rawValue = rawValue } public init(from decoder: Decoder) throws { let container = try decoder.singleValueContainer() try self.init(rawValue: container.decode(String.self)) } public func encode(to encoder: any Encoder) throws { var container = encoder.singleValueContainer() try container.encode(rawValue) } } } }

I understand that OpenAPI supports a lot of features, such as string formats, that can turn a simple feature into a very complex beast.

I also understand that not everybody has a real or strong need for strongly-types scalars. They could annoy some users ("All those raw values 🙄").

My previous experience with strongly-types scalars was the Swift GraphQL library Apollo: Custom Scalars. By default, it imports custom scalars as their raw Swift representation (so the URL above with also be a typealias to Swift.String). But it allows the developer to provide a custom implementation. I was able to replace all those raw String and Int with tagged values, with much happiness.

In the end, I wonder what is the opinion of the library maintainers on such a topic?