NSNumber.description(withLocale:) - cache the CFNumberFormatter when locale is nil

Author: spevans

Foundation/NSNumber.swift

@@ -536,6 +536,13 @@ open class NSNumber : NSValue {
         }
     }
 
+    private static let _numberFormatterForNilLocale: CFNumberFormatter = {
+        let formatter: CFNumberFormatter
+        formatter = CFNumberFormatterCreate(nil, CFLocaleCopyCurrent(), kCFNumberFormatterNoStyle)
+        CFNumberFormatterSetProperty(formatter, kCFNumberFormatterMaxFractionDigits, 15._bridgeToObjectiveC())
+        return formatter
+    }()
+
     open func description(withLocale locale: Locale?) -> String {
         // CFNumberFormatterCreateStringWithNumber() doesnt like SInt128Type as
         // it loses the type when looking it up and treats it as an SInt64Type
@@ -548,9 +555,7 @@ open class NSNumber : NSValue {
         let aLocale = locale
         let formatter: CFNumberFormatter
         if (aLocale == nil) {
-            formatter = CFNumberFormatterCreate(nil, CFLocaleCopyCurrent(), kCFNumberFormatterNoStyle)
-            CFNumberFormatterSetProperty(formatter, kCFNumberFormatterMaxFractionDigits, 15._bridgeToObjectiveC())
-
+            formatter = NSNumber._numberFormatterForNilLocale
         } else {
             formatter = CFNumberFormatterCreate(nil, aLocale?._cfObject, kCFNumberFormatterDecimalStyle)
         }