Optimization: AppFont main thread impact 5% -> 0.3%.

1Weather/UI/Helpers/AppFont.swift

@@ -19,24 +19,37 @@ public struct AppFont {
     }
     
     public struct SFPro {
+        private static var fontCache = [UIFont.Weight: [CGFloat: UIFont]]()
+        
+        static func font(weigth: UIFont.Weight, size: CGFloat) -> UIFont {
+            if let cached = fontCache[weigth]?[size] {
+                return cached
+            }
+            let descriptor = AppFont.fontDescriptor(size: size, weight: weigth)
+            let font = UIFont(descriptor: descriptor, size: size)
+            if fontCache[weigth] == nil {
+                fontCache[weigth] = [size: font]
+            }
+            else {
+                fontCache[weigth]![size] = font
+            }
+            return font
+        }
+        
         static func regular(size: CGFloat) -> UIFont {
-            let descriptor = AppFont.fontDescriptor(size: size, weight: .regular)
-            return UIFont(descriptor: descriptor, size: size)
+            font(weigth: .regular, size: size)
         }
         
         static func bold(size: CGFloat) -> UIFont {
-            let descriptor = AppFont.fontDescriptor(size: size, weight: .bold)
-            return UIFont(descriptor: descriptor, size: size)
+            font(weigth: .bold, size: size)
         }
         
         static func medium(size:CGFloat) -> UIFont {
-            let descriptor = AppFont.fontDescriptor(size: size, weight: .medium)
-            return UIFont(descriptor: descriptor, size: size)
+            font(weigth: .medium, size: size)
         }
         
         static func semibold(size: CGFloat) -> UIFont {
-            let descriptor = AppFont.fontDescriptor(size: size, weight: .semibold)
-            return UIFont(descriptor: descriptor, size: size)
+            font(weigth: .semibold, size: size)
         }
     }
 }