diff --git a/CleanClosureSyntax.xcodeproj/project.pbxproj b/CleanClosureSyntax.xcodeproj/project.pbxproj
index 8989692..19b1754 100644
--- a/CleanClosureSyntax.xcodeproj/project.pbxproj
+++ b/CleanClosureSyntax.xcodeproj/project.pbxproj
@@ -179,18 +179,18 @@
 			isa = PBXProject;
 			attributes = {
 				LastSwiftUpdateCheck = 0800;
-				LastUpgradeCheck = 0800;
+				LastUpgradeCheck = 0920;
 				ORGANIZATIONNAME = "Patrick Balestra";
 				TargetAttributes = {
 					AE2862D11D25568D00219753 = {
 						CreatedOnToolsVersion = 8.0;
-						DevelopmentTeam = 2EZDW5DVTJ;
+						DevelopmentTeam = ENLH686A45;
 						DevelopmentTeamName = "Patrick Balestra";
 						ProvisioningStyle = Automatic;
 					};
 					AE2862E71D2556DE00219753 = {
 						CreatedOnToolsVersion = 8.0;
-						DevelopmentTeam = 2EZDW5DVTJ;
+						DevelopmentTeam = ENLH686A45;
 						DevelopmentTeamName = "Patrick Balestra";
 						ProvisioningStyle = Automatic;
 					};
@@ -284,14 +284,22 @@
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
+				CLANG_WARN_BLOCK_CAPTURE_AUTORELEASING = YES;
 				CLANG_WARN_BOOL_CONVERSION = YES;
+				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_DOCUMENTATION_COMMENTS = YES;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
+				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
+				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
+				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
+				CLANG_WARN_STRICT_PROTOTYPES = YES;
+				CLANG_WARN_SUSPICIOUS_MOVE = YES;
 				CLANG_WARN_UNREACHABLE_CODE = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				CODE_SIGN_IDENTITY = "-";
@@ -331,14 +339,22 @@
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
+				CLANG_WARN_BLOCK_CAPTURE_AUTORELEASING = YES;
 				CLANG_WARN_BOOL_CONVERSION = YES;
+				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_DOCUMENTATION_COMMENTS = YES;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
+				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
+				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
+				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
+				CLANG_WARN_STRICT_PROTOTYPES = YES;
+				CLANG_WARN_SUSPICIOUS_MOVE = YES;
 				CLANG_WARN_UNREACHABLE_CODE = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				CODE_SIGN_IDENTITY = "-";
@@ -368,11 +384,12 @@
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				CODE_SIGN_IDENTITY = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
+				DEVELOPMENT_TEAM = ENLH686A45;
 				INFOPLIST_FILE = CleanClosureSyntax/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.patrickbalestra.CleanClosureSyntax;
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -383,11 +400,12 @@
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				CODE_SIGN_IDENTITY = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
+				DEVELOPMENT_TEAM = ENLH686A45;
 				INFOPLIST_FILE = CleanClosureSyntax/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.patrickbalestra.CleanClosureSyntax;
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
@@ -397,13 +415,14 @@
 				CODE_SIGN_ENTITLEMENTS = Cleaner/Cleaner.entitlements;
 				CODE_SIGN_IDENTITY = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
+				DEVELOPMENT_TEAM = ENLH686A45;
 				INFOPLIST_FILE = Cleaner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks @executable_path/../../../../Frameworks";
 				MACOSX_DEPLOYMENT_TARGET = 10.11;
 				PRODUCT_BUNDLE_IDENTIFIER = com.patrickbalestra.CleanClosureSyntax.Cleaner;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -413,13 +432,14 @@
 				CODE_SIGN_ENTITLEMENTS = Cleaner/Cleaner.entitlements;
 				CODE_SIGN_IDENTITY = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
+				DEVELOPMENT_TEAM = ENLH686A45;
 				INFOPLIST_FILE = Cleaner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks @executable_path/../../../../Frameworks";
 				MACOSX_DEPLOYMENT_TARGET = 10.11;
 				PRODUCT_BUNDLE_IDENTIFIER = com.patrickbalestra.CleanClosureSyntax.Cleaner;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
diff --git a/Cleaner/SourceEditorCommand.swift b/Cleaner/SourceEditorCommand.swift
index 1451699..4907e1b 100644
--- a/Cleaner/SourceEditorCommand.swift
+++ b/Cleaner/SourceEditorCommand.swift
@@ -9,12 +9,12 @@
 import Foundation
 import XcodeKit
 
-extension NSString {
+extension String {
     // Remove the given characters in the range
-    func remove(characters: [Character], in range: NSRange) -> NSString {
+    func remove(characters: [Character], in range: NSRange) -> String {
         var cleanString = self
         for char in characters {
-            cleanString = cleanString.replacingOccurrences(of: String(char), with: "", options: [.caseInsensitive], range: range) as NSString
+            cleanString = cleanString.replacingOccurrences(of: String(char), with: "", options: [.caseInsensitive], range: range as? Range) as String
         }
         return cleanString
     }
@@ -27,10 +27,10 @@ class SourceEditorCommand: NSObject, XCSourceEditorCommand {
         
         // Find lines that contain a closure syntax
         for lineIndex in 0 ..< invocation.buffer.lines.count {
-            let line = invocation.buffer.lines[lineIndex] as! NSString
+            let line = invocation.buffer.lines[lineIndex] as! String
             do {
                 let regex = try NSRegularExpression(pattern: "\\{.*\\(.+\\).+in", options: .caseInsensitive)
-                let range = NSRange(0 ..< line.length)
+                let range = NSRange(0 ..< line.count)
                 let results = regex.matches(in: line as String, options: .reportProgress, range: range)
                 // When a closure is found, clean up its syntax
                 _ = results.map { result in
@@ -39,7 +39,7 @@ class SourceEditorCommand: NSObject, XCSourceEditorCommand {
                     invocation.buffer.lines[lineIndex] = cleanLine
                 }
             } catch {
-                completionHandler(error as NSError)
+                completionHandler(error as Error)
             }
         }