error: generic parameter 'T' could not be inferred in swift

error: generic parameter 'T' could not be inferred in swift

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error: generic parameter 'T' could not be inferred in swift
Tag : ios , By : John Phipps
Date : November 15 2020, 03:01 PM

I hope this helps you . I have function which make flatted array from nested array. It works perfectly for int array. , You have to tell the compiler the type of T.
func makeFlatArrayGeneric<T>(_ array: [Any]) -> [T] {
    var flatArray = [T]()
    for item in array {
        if let item = item as? T {
        } else if let item = item as? [Any] {
            let result: [T] = makeFlatArrayGeneric(item)
            flatArray += result
    return flatArray

let array: [Any] = [1, 2, [3], [4, [5]]]
let items: [Int] = makeFlatArrayGeneric(array) //[1, 2, 3, 4, 5]
extension Array {
    func flatten() -> Array<Element> {
        return self.flatMap({ element -> [Element] in
            if let array = element as? Array {
                return array.flatten()
            } else {
                return [element]

let items: [Int] = array.flatten() //[1, 2, 3, 4, 5]

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Swift custom flatMap implementation causes error Generic parameter could not be inferred

Tag : swift , By : user171555
Date : March 29 2020, 07:55 AM
hope this fix your issue Something does not conform to NSObject.
Swift 4 automatically infers constraints for the generic parameter U used in your flatMap function by looking at all parameters which include U. U is used as a generic parameter to Wrapper which requires U: NSObject. Something is not a subclass of NSObject.

Initializing a Struct in Swift Error: Generic parameter could not be inferred

Tag : ios , By : Timbo
Date : March 29 2020, 07:55 AM
may help you . For a generic type, the generic parameter is actually considered to be part of the type. So the type of your struct isn't MyStruct, it's MyStruct (or whatever generic type you use. Therefore, you can't just declare the type by itself if there's not any information for the compiler to use to infer the actual type. Instead, you have to include the generic type in your declaration:
var myStruct: MyStruct?

Generic parameter 'A' could not be inferred (Swift 4, Bond and ReactiveKit frameworks migrating from Swift 2)

Tag : swift , By : Rob
Date : March 29 2020, 07:55 AM
With these it helps If you ever migrated from old versions of ReactiveKit/Bond implemented syntax, here is how to do it for your UIKit Reactive Extensions:
import UIKit
import Bond
import ReactiveKit

extension ReactiveExtensions where Base: UISearchBar {

    var delegate: ProtocolProxy {
        return base.protocolProxy(for: UISearchBarDelegate.self, setter: NSSelectorFromString("setDelegate:"))

    var text: DynamicSubject<String?> {

        let selector = #selector(UISearchBarDelegate.searchBar(_:textDidChange:))
        let textChanged = delegate.signal(for: selector) { (subj: SafePublishSubject<Void>, _: UISearchBar, _: NSString) in

        return dynamicSubject(
            signal: textChanged,
            get: { $0.text },
            set: { $0.text = $1 }

extension UISearchBar: BindableProtocol {

    public func bind(signal: SafeSignal<String?>) -> Disposable {
        return reactive.text.bind(signal: signal)

Generic parameter 'Self' could not be inferred swift

Tag : swift , By : tayles
Date : January 12 2021, 08:33 AM
hope this fix your issue 1) You have a comma that shouldn't be there. Also, you could use some spacing for readability, and you don't need the semicolon (though Swift will let you put it there):
print("ISBN: " + self.currentISBN! + "  ID:" + book_id! + " Title:" + book_title!)
print("ISBN: \(self.currentISBN!)  ID:\(book_id!) Title:\(book_title!)")

Generic parameter 'Self' could not be inferred (swift 4)

Tag : xcode , By : OlioEngr
Date : March 29 2020, 07:55 AM
With these it helps range(of / index(of returns an optional. You have to unwrap the optional in the range expression
extension String
    func substringToFirstChar(of char: Character) -> String?
        guard let pos = self.range(of: String(char))?.lowerBound else { return nil }
        // or  guard let pos = self.index(of: char) else { return nil }
        let subString = self[..<pos]
        return String(subString)
extension String
    func substringToFirstChar(of char: Character) -> String
        guard let pos = self.range(of: String(char))?.lowerBound else { return self }
        // or  guard let pos = self.index(of: char) else { return self }
        let subString = self[..<pos]
        return String(subString)
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