ProtocolWithLocalStruct.swift

protocol SomeProtocol {
    associatedtype SomeType: Decodable
    
    var bar: String { get }
}

struct Foo: SomeProtocol {
    struct SomeType: Decodable {
        let bar: String
    }
            
    var bar: String
}

struct Foo2: SomeProtocol {
    typealias SomeType = Bool
    
    var bar: String
}