在 SWIFT 字符串插值中没有更多上下文的表达式类型不明确

Question

I have React Native project. And I need in the native part of IOS to make string interpolation of formattedValue with a character, but I get the error "Type of expression is ambiguous without more context", and if I try the same code in the playground everything is working with out error. I'm not so experienced in SWIFT, can you tell me please why I get this error? And which the best way to make a string interpolation?

import Foundation
import SciChart.Protected.SCILabelProviderBase

class SCIAxisNumericLabelProvider: SCILabelProviderBase<ISCINumericAxis> {
    var format: String?
    var specialChar: String?

    init(format: String?) {
        let pattern = "[^0-9.]"
        let regex = try! NSRegularExpression(pattern: pattern)
        let formatValue = regex.stringByReplacingMatches(in: format ?? "", range: NSMakeRange(0, format?.count ?? 0), withTemplate: "")

        self.format = formatValue
        self.specialChar = format?.replacingOccurrences(of: "\(formatValue)", with: "")
        
        super.init(axisType: ISCINumericAxis.self)
    }

    override func formatLabel(_ dataValue: ISCIComparable!) -> ISCIString! {
        let dataValueToDouble = dataValue.toDouble()
        let formattedValue = NSString(format: NSString(string: self.toFormat()), dataValueToDouble == -0 ? 0 : dataValueToDouble)
        
        if let char = specialChar {
            return "\(formattedValue) \(NSString(char))" // Here I get the error Type of expression is ambiguous without more context
        }
        
        return formattedValue
    }

    override func formatCursorLabel(_ dataValue: ISCIComparable!) -> ISCIString! {
      return formatLabel(dataValue)
    }

    func toFormat() -> String {
        if (self.format != nil) {
            let a = self.format!.split(separator: ".")
             if (a.count > 1) {
                return "%0." + String(a[1].count) + "f"
             }
         }
        return "%0.f"
    }
    
    func extractSpecialChar(value: String) {
        
    }
}

Answer 1

In the end of the day I decided this error, I separated string interpolation and converting:

    override func formatLabel(_ dataValue: ISCIComparable!) -> ISCIString! {
        let formatterValue = self.toFormat();
        let valueDouble = dataValue.toDouble()
        let valueDoubleExcludedNegZero = valueDouble == -0 ? 0 : valueDouble
        let precisionString = String(format: formatterValue, valueDoubleExcludedNegZero)

        if let char = specialChar {
            let resultString = precisionString + " " + char
            return NSString(string: resultString)
        }

        return NSString(string: precisionString)
    }