Type of expression is ambiguous without more context Swift

问题

I am getting a 'Type of expression is ambiguous without more context ' on this part of code from a project I am trying to upgrade to latest Swift version. I can't seem to figure it out. I tried different things but can't get it to work.

The problem is on the syntax of this line

let imageToDeleteParameters  = imagesToDelete.map { ["id": $0.id, "url": $0.url.absoluteString, "_destroy": true] }

Full code:

extension TutorialCreationRequest: WebserviceParametrable {
    func toParameters() -> [String: AnyObject] {
        let imageParameters = images.map { ["url": $0] }
        let imageToDeleteParameters  = imagesToDelete.map { ["id": $0.id, "url": $0.url.absoluteString, "_destroy": true] }
        return [
            "title": title,
            "is_draft": isDraft,
            "difficulty": difficulty,
            "duration": duration,
            "cost": cost,
            "user_id": userId,
            "description": description,
            "to_sell": toSell,
            "images": [imageParameters, imageToDeleteParameters].flatMap { $0 }
        ]
    }
}

回答1:

Not an answer to this question, but as I came here looking for the error others might find this also useful:

For me, I got this Swift error when I tried to use the for (index, object) loop on an array without adding the .enumerated() part ...

回答2:

This happens when you have a function with wrong argument names.

Example:

functionWithArguments(argumentNameWrong: , argumentName2: )

and You declared your function as:

functionWithArguments(argumentName1: , argumentName2: ){}

This usually happens when you changed the name of a Variable. Make sure you refactor when you do that.

回答3:

The compiler can't figure out what type to make the Dictionary, because it's not homogenous. You have values of different types. The only way to get around this is to make it a [String: Any], which will make everything clunky as all hell.

return [
    "title": title,
    "is_draft": isDraft,
    "difficulty": difficulty,
    "duration": duration,
    "cost": cost,
    "user_id": userId,
    "description": description,
    "to_sell": toSell,
    "images": [imageParameters, imageToDeleteParameters].flatMap { $0 }
] as [String: Any]

This is a job for a struct. It'll vastly simplify working with this data structure.

回答4:

I had this message when the type of a function parameter didn't fit. In my case it was a String instead of an URL.

回答5:

I got this error when I put a space before a comma in the parameters when calling a function.

eg, I used:

myfunction(parameter1: parameter1 , parameter2: parameter2)

Whereas it should have been:

myfunction(parameter1: parameter1, parameter2: parameter2)

Deleting the space got rid of the error message

回答6:

Explicitly declaring the inputs for that mapping function should do the trick:

let imageToDeleteParameters  = imagesToDelete.map {
    (whatever : WhateverClass) -> Dictionary<String, Any> in
    ["id": whatever.id, "url": whatever.url.absoluteString, "_destroy": true]
}

Substitute the real class of "$0" for "WhateverClass" in that code snippet, and it should work.

回答7:

In my case, this error message shown when I don't added optional property to constructor.

struct Event: Identifiable, Codable {

    var id: String
    var summary: String
    var description: String?
    // also has other props...

    init(id: String, summary: String, description: String?){
        self.id = id
        self.summary = summary
        self.description = description
    }
}

// skip pass description
// It show message "Type of expression is ambiguous without more context"
Event(
    id: "1",
    summary: "summary",
)

// pass description explicity pass nil to description
Event(
    id: "1",
    summary: "summary",
    description: nil
)

but it looks always not occured.

I test in my playground this code, it show warning about more concrete

var str = "Hello, playground"
struct User {
    var id: String
    var name: String?
    init(id: String, name: String?) {
        self.id = id
        self.name = name
    }
}

User(id: "hoge") // Missing argument for parameter 'name' in call

回答8:

You have two " " before the =

let imageToDeleteParameters = imagesToDelete.map { ["id": $0.id, "url": $0.url.absoluteString, "_destroy": true] }

来源：https://stackoverflow.com/questions/40894582/type-of-expression-is-ambiguous-without-more-context-swift