How to work with swift protocols in models

Question

JSON:

"sittingFurniture":[
{
    "sittingObjectType": "chair",
    "fabric": "textile"
},
{
    "sittingObjectType":"bed",
    "height": 70
},
...
]

Swift code:

protocol SittingObject {
    var type: SittingObjectType
}

public enum SittingObjectType: Codable, Equatable {
    case chair
    case sofa
    case bed
}

struct FancyChair: SittingObject, Codable, Equatable  {
    let fabric: String
    let type: SittingObjectType = .chair
}

struct FancyBed: SittingObject, Codable, Equatable{
    let height: Int
    let type: SittingObjectType = .bed
}

struct FurnitureList: Codable, Equatable {
    let sittingFurniture: [SittingObject] //ERROR
}

Protocol 'SittingObject' can only be used as a generic constraint because it has Self or associated type requirements

How can we best deserialize such JSON?

Answer 1

It might be better to set up your structure like this, instead of two separate objects.

Then you might be able to use JSONDecoder on FurnitureList

    struct FancyFurnitureObject: SittingObject, Codable, Equatable  {
        let fabric: String?
        let height: Int?
        let type: SittingObjectType
    }
    
    public enum SittingObjectType: Codable, Equatable {
        case chair
        case sofa
        case bed
    }
    
    struct FurnitureList: Codable, Equatable {
        let sittingFurniture: [FancyFurnitureObject] //ERROR
    }