Create a reusable file decoder with different Models

I can have multiple models and they could be within an array or not, for example:

[Model1] or Model or [Model2] or [String: [Model2]]

This is my attempt to reuse the same function:

/// Decode existing file on disk
func decodeFileStoredInDisk(modelToDecode: Any, fileName: String, fileExtension: String) -> Any? {
    var decodedFile: Any = []
    
    do {
        let fileURL = try FileManager.default
            .url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
            .appendingPathComponent(fileName + fileExtension)
        
        let data = try Data(contentsOf: fileURL)
        decodedFile = try JSONDecoder().decode(modelToDecode.self, from: data)
        
    } catch {
        print("🛑 Error decoding file disk: \(error)")
    }
    
    return decodedFile
}

The problem I’m having is that it complains:

Cannot convert value of type 'Any' to expected argument type 'Any.Protocol'

I tried the suggestion:

decodedFile = try JSONDecoder().decode(modelToDecode.self as! Any.Protocol, from: data)

but still complains with:

Protocol 'Any' as a type cannot conform to 'Decodable'

The error is in modelToDecode, if I put the exact model: [Model1] it likes that.

How can I use any type there?

>Solution :

The decoder needs to know the static type therefore Any is not supported at all.

Use a generic type constrained to Decodable like this

func decodeFileStoredInDisk<T : Decodable>(modelToDecode: T.Type, fileName: String, fileExtension: String) throws -> T {
    let fileURL = try FileManager.default
        .url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
        .appendingPathComponent(fileName)
        .appendingPathExtension(fileExtension)
        
    let data = try Data(contentsOf: fileURL)
    return try JSONDecoder().decode(T.self, from: data)
}

And the function passes a possible error to the caller.