flatMap and `Ambiguous reference to member` error

Question

Consider the following code:

typealias PersonRecord = [String : AnyObject]

struct Person {
    let name: String
    let age: Int

    public init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

extension Person {
    init?(record : PersonRecord) {
        guard let name = record["name"] as? String,
        let age = record["age"] as? Int else {
            return nil
        }

        self.name = name
        self.age = age
    }
}

Now I want to create an array of Persons from an array of Records:

let records = // load file from bundle
let persons = records.flatMap(Person.init)

But I get the following error:

error: ambiguous reference to member 'init(name:age:)'

If I move the failable initializer out of the extension, I still get the same error.

What am I missing here, is this not a correct usage of flatMap?

EDIT - solved:

Found the error: the code that read in the records file from disk, returned the wrong type. Once I fixed that, the error went away.

Compiles fine for me, assuming `records` is of type `[PersonRecord]`. As with all weird compiler errors, try cleaning your build folder – and if you're in a playground, try it in a full project. — Hamish, Oct 22 '16 at 19:22
That's good to know; I moved that code to a brand new PlayGround, and no errors. How do I clean the build folder for a playground, if any? — koen, Oct 22 '16 at 19:44
I don't believe you can (at least not easily) in a playground. Personally, I would avoid using playgrounds to begin with, as they're notoriously buggy – a full project is a much better Swift environment. — Hamish, Oct 22 '16 at 19:56
Hmm, I moved the whole playground code (of which the above was just a short snippet) to a full project, and am still getting the error. So something else is going on. `Person` actually confirms to a protocol (`Nameable`, which only has one property: `name`), could that interfere? — koen, Oct 22 '16 at 20:08
Not from what I can tell – although in any case it would be really helpful if you could reduce your code down to a [mcve], and update the question with that example. — Hamish, Oct 22 '16 at 20:15

score 3 · Accepted Answer · answered Oct 22 '16 at 21:18

For this to work

let persons = records.flatMap(Person.init)

the param passed to the flatMap closure must be the same type received by Person.init, so it must be PersonRecord.

Then records must be a list of PersonRecord, something like this

let records: [PersonRecord] = []

Now it works

let persons = records.flatMap(Person.init)

score 1 · Answer 2 · answered Aug 10 '17 at 14:04

1

Most of the times the Ambiguous reference to member in a map or flatMap is because the return type isn't specified

array.flatMap({ (item) -> ObjectToReturn? in })

answered Aug 10 '17 at 14:04

Jeremy Piednoel

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flatMap and `Ambiguous reference to member` error

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