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Objective-C

Objective-C. Drew Cheng CS420. Overview. True superset of ANSI C Object-Oriented methods from SmallTalk There is no formal written standard for the language Relies on outside libraries Iterative/Imperative Flexibility, most things are done at runtime Dynamic Typing Dynamic Binding

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Objective-C

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  1. Objective-C Drew Cheng CS420

  2. Overview • True superset of ANSI C • Object-Oriented methods from SmallTalk • There is no formal written standard for the language • Relies on outside libraries • Iterative/Imperative • Flexibility, most things are done at runtime • Dynamic Typing • Dynamic Binding • Dynamic Linking • Message Passing

  3. History • Created by Brad Cox and Tom Love at their company Stepstone • Both were introduced to SmallTalk while working at ITT • Cox was interested in the problems of true reusability in software design and programming • Modified C compiler and created a Object-Oriented extension of C called OOPC • Tom Love added more to OOPC from SmallTalk creating Objective-C

  4. 1986 – Stepstone releases Objective-C • 1988 – Steve Jobs acquires Objective-C license for NeXT • NeXT releases their own Objective-C compiler and libraries used in NeXTstep Operating System and OpenStep API • 1993 – GNU Objective-C runtime, currently in use, created by Kresten Thorup • 1996 – Apple Inc. acquires NeXT and uses OpenStep in new Mac OS X • Apple combines Objective-C and NeXT’s Objective-C, creates Cocoa API, most significant environment

  5. Uniqueness • Messaging/Forwarding • Does not call method, sends message • Target of message is resolved at runtime • Message passing has no type checking • Receiver not guaranteed to respond. No response either return null pointer or “forward” to an object that will respond • Initial interpretation of message in Objc-C 3x longer than C++ virtual method call. Messages are cached and subsequent calls 50% faster than C++ method call. • Categories/Protocols

  6. Primitives • Int, float, double, char • Unsigned, signed, short, long, long long • id – Generic object type • Can be used to store any object • Essential to Objective-C’s dynamic binding • If/Else Statements, For/While/Do Loops • Combine features by nesting, “and/or” conditionals • Abstraction – variables, functions, classes

  7. Functions

  8. Variable Passing • Default method is pass-by-value for primitive data types • Objects use pass-by-reference • Impossible to use pass-by-value for Objects • Does not pass by result, value-result, name, or need

  9. Type Checking • Dynamic type checking • Considered weak typed language • Language supports coercion • When adding float and int, one is changed • Does not support type inference

  10. Object-Oriented • Does not support multiple inheritance • Class must inherit from Object/NSObject class • Variable inheritance is dynamic • Method inheritance is dynamic • The super-method invocation uses method from class that super is called in (dynamic) • No operation and method overloading

  11. Conclusion • Very easy to learn • Simple way of handling classes and objects • Dynamism allows flexibility in code • Errors may are not found until runtime • Not a very used language outside Apple

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