Swift is a general-purpose, multi-paradigm, compiled programming language created for iOS, OSX, watchOS, tvOS and Linux development by Apple Inc. Swift is designed to work with Apple's Cocoa and Cocoa Touch frameworks and the large body of existing Objective-C code written for Apple products. Swift is intended to be more resilient to erroneous code ("safer") than Objective-C and also more concise. It is built with the LLVM compiler framework included in Xcode 6 and later and uses the Objective-C runtime, which allows C, Objective-C, C++ and Swift code to run within a single program.Swift supports the core concepts that made Objective-C flexible, notably dynamic dispatch, widespread late binding, extensible programming and similar features. These features also have well known performance and safety trade-offs, which Swift was designed to address. For safety, Swift introduced a system that helps address common programming errors like null pointers, as well as introducing syntactic sugar to avoid the pyramid of doom that can result. For performance issues, Apple has invested considerable effort in aggressive optimization that can flatten out method calls and accessors to eliminate this overhead. More fundamentally, Swift has added the concept of protocol extensibility, an extensibility system that can be applied to types, structs and classes, Apple promotes this as a real change in programming paradigms they refer to as "protocol-oriented programming".