Type of expression is ambiguous without more context Swift


Swift Problem Overview

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 }

Swift Solutions

Solution 1 - Swift

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


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.

Solution 2 - Swift

This can happen if any part of your highlighted method or property is attempting to access a property or method with the incorrect type.

Here is a troubleshooting checklist, make sure:

  • the type of arguments match in the call site and implementation.
  • the argument names match in the call site and implementation.
  • the method name matches in the call site and implementation.
  • the returned value of a property or method matches in the usage and implementation (ie: enumerated())
  • you don't have a duplicated method with potentially ambiguous types such as with protocols or generics.
  • the compiler can infer the correct type when using type inference.

A Strategy

  • Try breaking apart your method into a greater number of simpler method/implementations.

For example, lets say you are running compactMap on an array of custom Types. In the closure you are passing to the compactMap method, you initialize and return another custom struct. When you get this error, it is difficult to tell which part of your code is offending.

  • For debugging purposes, you can use a for in loop instead of compactMap.
  • instead of passing the arguments, directly, you can assign them to constants in the for loop.

By this point, you may come to a realization, such as, instead of the property you thought you wanted to assign actually had a property on it that had the actual value you wanted to pass.

Solution 3 - Swift

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 ...

Solution 4 - Swift

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.

Solution 5 - Swift

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.

Solution 6 - Swift

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.

Solution 7 - Swift

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

Solution 8 - Swift

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"
    id: "1",
    summary: "summary",

// pass description explicity pass nil to description
    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

Solution 9 - Swift

For me the case was Type inference I have changed the function parameters from int To float but did not update the calling code, and the compiler did not warn me on wrong type passed to the function


func myFunc(param:Int, parma2:Int) {}


func myFunc(param:Float, parma2:Float) {}

Calling code with error

var param1:Int16 = 1
var param2:Int16 = 2
myFunc(param:param1, parma2:param2)// error here: Type of expression is ambiguous without more context

To fix:

var param1:Float = 1.0f
var param2:Float = 2.0f
myFunc(param:param1, parma2:param2)// ok!

Solution 10 - Swift

My problem were the parameters without default value

I changed

let contaPadrao = RedeConta(agencia: cPadrao?.agencia,
                                    conta: cPadrao?.conta,
                                    dac: cPadrao?.dac)


let contaPadrao = RedeConta(agencia: cPadrao?.agencia ?? "",
                                    conta: cPadrao?.conta ?? "",
                                    dac: cPadrao?.dac ?? "")

Solution 11 - Swift

You have two " " before the =

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

Solution 12 - Swift

In my case it happened with NSFetchedResultsController and the reason was that I defined the NSFetchedResultsController for a different model than I created the request for the initialization (RemotePlaylist vs. Playlist):

  var fetchedPlaylistsController:NSFetchedResultsController<RemotePlaylist>!

but initiated it with a request for another Playlist:

let request = Playlist.createFetchRequest()
fetchedPlaylistsController = NSFetchedResultsController(fetchRequest: request, ...

Solution 13 - Swift

In my case, I ran into this error when I was creating a distribution build, and a class was referring to Debug only context method.

Something like this. Try compiling the below class for the Distribution build.

class MyClass {
   func sayHello() {
   #if DEBUG
    func helloWorld() {
         print("Hello world")

Solution 14 - Swift

In my case, the arguments I was passing had optional String values. Providing a default value to fall back on ( in case the value is nil ) solved this issue for me.

I changed this -

gitHubRepositoryOwnerName: gitHubRepositoryDetails?[index].owner?.login,
gitHubRepositoryName: gitHubRepositoryDetails?[index].name,
avatarUrl: gitHubRepositoryDetails?[index].owner?.avatar_url)

to this -

gitHubRepositoryOwnerName: gitHubRepositoryDetails?[index].owner?.login ?? "",
gitHubRepositoryName: gitHubRepositoryDetails?[index].name ?? "",
avatarUrl: gitHubRepositoryDetails?[index].owner?.avatar_url ?? "")

Solution 15 - Swift

Make sure if there is any delegate methods are available with extension, then implement those and error will disappear.

Solution 16 - Swift

This error could be shown due to multiple reasons. One of the most prominent reasons is a type mismatch. For example,

Suppose, parameter icons is a type of array and we passed an Enum as IconDismiss.

## Wrong
text.config = TextField.Config(isClearable: true, icons: IconDismiss)
## Correct
text.config = TextField.Config(isClearable: true, icons: [IconDismiss])

Solution 17 - Swift

As theEye's answer it is not an answer to this question, but as I also came here looking for the error im posting my case as others might find this also useful:

I got this error message when I was by error trying to calculate a value of two different types.

In my case I was trying to divide a CGFloat by a Double


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