diff --git a/ObjectMapper.xcodeproj/project.pbxproj b/ObjectMapper.xcodeproj/project.pbxproj
index 89817b2e..1394cc3c 100644
--- a/ObjectMapper.xcodeproj/project.pbxproj
+++ b/ObjectMapper.xcodeproj/project.pbxproj
@@ -995,7 +995,7 @@
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SDKROOT = appletvos;
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = 3;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1024,7 +1024,7 @@
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SDKROOT = appletvos;
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = 3;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1043,7 +1043,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.hearst.ObjectMapper-tvOSTests";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = appletvos;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 			};
 			name = Debug;
@@ -1061,7 +1061,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.hearst.ObjectMapper-tvOSTests";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = appletvos;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 			};
 			name = Release;
@@ -1087,7 +1087,7 @@
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SDKROOT = watchos;
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = 4;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1115,7 +1115,7 @@
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SDKROOT = watchos;
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = 4;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1172,7 +1172,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
@@ -1221,7 +1221,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VALIDATE_PRODUCT = YES;
 				VERSIONING_SYSTEM = "apple-generic";
@@ -1244,7 +1244,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.hearst.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_SWIFT3_OBJC_INFERENCE = On;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Default;
 				SWIFT_VERSION = 4.0;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1266,7 +1266,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.hearst.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_SWIFT3_OBJC_INFERENCE = On;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Default;
 				SWIFT_VERSION = 4.0;
 				TVOS_DEPLOYMENT_TARGET = 9.0;
 				WATCHOS_DEPLOYMENT_TARGET = 2.0;
@@ -1285,7 +1285,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "com.heart.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_SWIFT3_OBJC_INFERENCE = On;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Default;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
@@ -1298,7 +1298,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "com.heart.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_SWIFT3_OBJC_INFERENCE = On;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Default;
 				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
@@ -1374,7 +1374,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.heart.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -1391,7 +1391,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.heart.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;
-				SWIFT_VERSION = 3.1;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
diff --git a/Sources/HexColorTransform.swift b/Sources/HexColorTransform.swift
index 9053909a..ac045a32 100644
--- a/Sources/HexColorTransform.swift
+++ b/Sources/HexColorTransform.swift
@@ -35,7 +35,7 @@ open class HexColorTransform: TransformType {
 	open func transformFromJSON(_ value: Any?) -> Object? {
 		if let rgba = value as? String {
 			if rgba.hasPrefix("#") {
-				let index = rgba.characters.index(rgba.startIndex, offsetBy: 1)
+				let index = rgba.index(rgba.startIndex, offsetBy: 1)
 				let hex = String(rgba[index...])
 				return getColor(hex: hex)
 			} else {
@@ -89,7 +89,7 @@ open class HexColorTransform: TransformType {
 		let scanner = Scanner(string: hex)
 		var hexValue: CUnsignedLongLong = 0
 		if scanner.scanHexInt64(&hexValue) {
-			switch (hex.characters.count) {
+			switch (hex.count) {
 			case 3:
 				red   = CGFloat((hexValue & 0xF00) >> 8)       / 15.0
 				green = CGFloat((hexValue & 0x0F0) >> 4)       / 15.0
diff --git a/Sources/ToJSON.swift b/Sources/ToJSON.swift
index 32c34323..bb53f611 100644
--- a/Sources/ToJSON.swift
+++ b/Sources/ToJSON.swift
@@ -34,14 +34,14 @@ private func setValue(_ value: Any, map: Map) {
 
 private func setValue(_ value: Any, key: String, checkForNestedKeys: Bool, delimiter: String, dictionary: inout [String : Any]) {
 	if checkForNestedKeys {
-		let keyComponents = ArraySlice(key.components(separatedBy: delimiter).filter { !$0.isEmpty }.map { $0.characters })
+		let keyComponents = ArraySlice(key.components(separatedBy: delimiter).filter { !$0.isEmpty }.map { $0 })
 		setValue(value, forKeyPathComponents: keyComponents, dictionary: &dictionary)
 	} else {
 		dictionary[key] = value
 	}
 }
 
-private func setValue(_ value: Any, forKeyPathComponents components: ArraySlice<String.CharacterView.SubSequence>, dictionary: inout [String : Any]) {
+private func setValue(_ value: Any, forKeyPathComponents components: ArraySlice<String>, dictionary: inout [String : Any]) {
 	if components.isEmpty {
 		return
 	}