Made the code compatible with Swift 4.2 by doing the following,

Replaced the method UIImagePNGRepresentation(self) with self.pngData()
Replaced the method UIImageJPEGRepresentation(self, 1.0) with self.jpegData(compressionQuality: 1.0)

Author: rizwan95

Cache.xcodeproj/project.pbxproj

@@ -1027,6 +1027,7 @@
 				SDKROOT = appletvos;
 				SKIP_INSTALL = YES;
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = 3;
 				TVOS_DEPLOYMENT_TARGET = 9.2;
 			};
@@ -1052,6 +1053,7 @@
 				PRODUCT_NAME = Cache;
 				SDKROOT = appletvos;
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = 3;
 				TVOS_DEPLOYMENT_TARGET = 9.2;
 			};
@@ -1143,6 +1145,7 @@
 				PRODUCT_NAME = Cache;
 				SDKROOT = macosx;
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Debug;
 		};
@@ -1165,6 +1168,7 @@
 				PRODUCT_NAME = Cache;
 				SDKROOT = macosx;
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Release;
 		};
@@ -1250,7 +1254,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 4.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
@@ -1302,7 +1306,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-				SWIFT_VERSION = 4.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VALIDATE_PRODUCT = YES;
 				VERSIONING_SYSTEM = "apple-generic";
@@ -1326,6 +1330,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = no.hyper.Cache;
 				PRODUCT_NAME = Cache;
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Debug;
 		};
@@ -1345,6 +1350,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = no.hyper.Cache;
 				PRODUCT_NAME = Cache;
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Release;
 		};

Source/iOS/UIImage+Extensions.swift

@@ -23,7 +23,7 @@ extension UIImage {
   /// Convert to data
   func cache_toData() -> Data? {
     return hasAlpha
-      ? UIImagePNGRepresentation(self)
-      : UIImageJPEGRepresentation(self, 1.0)
+      ? self.pngData()
+      : self.jpegData(compressionQuality: 1.0)
   }
 }