Hi folks. I am facing the following situation:
My application defines a contract through a protocol:
public protocol Project {
var name: String
}
The application uses an external Obj-C library which provides a compatible type:
@interface CProject : NSObject
@property (nonatomic, readonly, nonnull) NSString *name;
@end
The intention is to use the existential any Project throughout my application, so as to hide the concrete business implementation from the view. To that end, I can:
extension CProject: Project {}
Fantastic.
However, we run into an unfortunate quirk in Swift when we try to import the following perfectly conforming type:
@interface CTask : NSObject
@property (nonatomic, readonly, nonnull) CProject *project;
@end
public protocol Task {
var project: any Project
}
extension CTask: Task {} // type 'CTask' does not conform to protocol 'Task'
In reality, of course, CProject is perfectly conforming to any Project, so implicitly downcasting CProject to the existential Project in the compiler would solve the problem. Alas, this is not how Swift works right now. I need to declare the type explicitly:
extension CTask: Task {
var project: any Project { /* magic */ }
}
The question now becomes: is there any way for me to access the project: CProject on CTask that I just shadowed in my extension, in order to pass it back at this level? Is this sane?
Related: Using subtypes in the implementation of protocol properties and function return values