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Unable to infer type when returning a function

By : IcarusFox
Date : August 01 2020, 09:00 AM
around this issue So the issue which you are facing is - by design how TS works. Type inference is done from left to right, from top to bottom. Also common sense here shows that your requirement is not possible as if you say K extends keyof T then K is never until T is known, as when you set key you have no object yet provided then at the type level you have exactly:
code :
type K = keyof unknown; // K is never
const propEq = <K extends PropertyKey, V>(key: K, equals: V) => 
<T extends Record<K, V>>(object: T) => object[key] === equals;

propEq3('a', 1)({a: 2}) // yes correct
propEq3('a', 1)({a: 'str'}) // error as it should, `a` has different type
propEq3('a', 1)({b: 1}) // error as it should, there is no `a` in object

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Is the C# compiler unable to infer method type parameters by expected return type?

By : user2619832
Date : March 29 2020, 07:55 AM
Hope that helps Check C# Language Specification §7.5.2, the declaring type of a variable is not an attestation for type inference, and obviously it shouldn't be. Consider the following code:
code :
Base b = Test<Derived>();
Derived d = Test<Derived>();

error: unable to infer enough type information about `_`; type annotations required

By : Sean
Date : March 29 2020, 07:55 AM
will be helpful for those in need Replace impl with just impl. You don't want a generic impl, you want a specific impl. You'd write impl to define type parameters that you can use later in the impl; you don't need that here.
When you write impl, this f64 is interpreted as a type parameter. However, all other occurrences of f64 in the impl are interpreted as the f64 keyword, which designates the primitive f64 type. The compiler is complaining because it is not able to infer a concrete type for the f64 type parameter.

Why is TypeScript unable to infer the type of function parameters when implementing a generic interface?

By : L.Dix
Date : March 29 2020, 07:55 AM
wish of those help When implementing the ITransformer interface you can override transform with different signatures, for example:
code :
class Transformer implements ITransformer<Input, Output> {
    transform(input: string): Output;
    transform(input: number): Output;
    transform(input: Input): Output;
    transform(input: any): Output {
        // ...
transform = (input: Input) => new Output(input.name);
transform = (input: Test) => new Test();
class Test {
    method1() { }

    method2 = () => {}
var Test = (function () {
    function Test() {
        this.method2 = function () { };
    Test.prototype.method1 = function () { };
    return Test;

Unable to infer complex closure return type; add explicit type to disambiguate

By : Poyer
Date : March 29 2020, 07:55 AM
seems to work fine Does anybody know how I can solve this error that I'm getting? The error is received on the first line in the following chunk of code: , Try adding the return type in the closure like this code:
code :
let fetchedResultsController: NSFetchedResultsController = { () -> NSFetchedResultsController<NSFetchRequestResult> in
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Message")
    let delegate = UIApplication.shared.delegate as! AppDelegate
    let context = delegate.persistentContainer.viewContext
    let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    return frc

Unable to infer complex closure return type; add explicit type to disambiguate in RxSwift

By : Reet Bons
Date : March 29 2020, 07:55 AM
wish of those help This was an interesting one! The take-away here is that when you are in doubt, go ahead and make your own operator. If it turns out that you later figure out how to do the job using the built-in operators, then you can replace yours. The only thing with making your own is that they require a lot more testing.
Note, to use the below, you will have to combineLatest of your observables and then flatMap and pass their values into this function.
code :
// all possible results from this job.
enum ProcessResult {
    case success
    case deleteFailure(Error)
    case imageFailue(Error)
    case backImageFailure(Error)
    case documentFailure(Error)

func uploadContent(apiClient: APIClient, documentID: Int, frontImage: UIImage, backImage: UIImage, parameters: Parameters) -> Single<ProcessResult> {
    // instead of trying to deal with all the materializes, I decided to turn it into a single process.
    return Single.create { observer in

        // each api call happens in turn. Note that there are no roll-back semantics included! You are dealing with a very poorly written server.
        let deleted = apiClient.deleteDocument(id: documentID)

        let imagesUploaded = deleted
            .flatMap { _ in Observable.zip(apiClient.uploadImage(image: frontImage).asObservable(), apiClient.uploadImage(image: backImage).asObservable()) }

        let documentUploaded = imagesUploaded
            .flatMap { arg -> Single<Void> in
                let (frontURL, backURL) = arg
                var updatedParams = parameters
                // add frontURL and backURL to parameters
                return apiClient.uploadDocument(parameters: updatedParams)

        let disposable = deleted
            .subscribe(onError: { observer(.success(ProcessResult.deleteFailure($0))) })
        let disposable1 = imagesUploaded
            .subscribe(onError: { observer(.success(ProcessResult.imageFailue($0))) })
        let disposable2 = documentUploaded
                onNext: { observer(.success(ProcessResult.success)) },
                onError: { observer(.success(ProcessResult.documentFailure($0))) }

        return Disposables.create([disposable, disposable1, disposable2])
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