CODEWITHSUNDEEP
jsonswiftgenericsdecodingcodable
NG235
NG235

Reputation: 1271

Swift - Argument type does not conform to expected type

I am trying to make a reusable JSON decoder in my Swift app, but am getting the following errors when running:

My code is below:

func decode<T: Codable>(_ type: T.Type, from: String) -> [T] {
    let url = URL(fileURLWithPath: from)
    let data = try? Data(contentsOf: url)
    let result = try? JSONDecoder().decode([T].self, from: data!)
    return result!
}
print(decode(User.self, from: "data.json")

Thank you for assisting me in solving this problem.

Best Regards, NG253

Upvotes: 1

Views: 4087

Answers (1)

Joakim Danielson
Joakim Danielson

Reputation: 51872

You don't need to pass the type as an argument if the return type is known to the compiler

Here is my version (using a local string)

func decode<T: Decodable>(from: String) throws -> [T] {
    //let url = URL(fileURLWithPath: from)
    //let data = try? Data(contentsOf: url)
    let data = from.data(using: .utf8)!
    return try JSONDecoder().decode([T].self, from: data!)
}

struct User: Decodable {
    let name: String
}

let str = """
   [{"name": "abc"}]
"""

do {
    let users: [User] = try decode(from: str)
} catch {
    print(error)
}

Upvotes: 1

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