18 Facts About Objective-C

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.

Objective-C was the standard programming language supported by Apple for developing macOS and iOS applications using their respective application programming interfaces, Cocoa and Cocoa Touch, until the introduction of Swift in 2014.

Objective-C was created primarily by Brad Cox and Tom Love in the early 1980s at their company Productivity Products International.

Objective-C realized that a language like Smalltalk would be invaluable in building development environments for system developers at ITT.

Objective-C soon had a working implementation of an object-oriented extension to the C language, which he called "OOPC" for Object-Oriented Pre-Compiler.

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The GNU Objective-C runtime, which has been in use since 1993, is the one developed by Kresten Krab Thorup when he was a university student in Denmark.

The Smalltalk-style programming as used in Objective-C allows messages to go unimplemented, with the method resolved to its implementation at runtime.

Objective-C requires that the interface and implementation of a class be in separately declared code blocks.

Objective-C was extended at NeXT to introduce the concept of multiple inheritance of specification, but not implementation, through the introduction of protocols.

Objective-C makes use of ad hoc protocols called informal protocols and compiler-enforced protocols called formal protocols.

Objective-C borrowed and extended the concept of categories from Smalltalk implementations to help with this process.

All Objective-C applications developed for macOS that make use of the above improvements for Objective-C 2.

Objective-C today is often used in tandem with a fixed library of standard objects, such as Cocoa, GNUstep or ObjFW.

Objective-C allows for the declaration of new root classes that do not inherit any existing functionality.

Originally, Objective-C-based programming environments typically offered an Object class as the base class from which almost all other classes inherited.

Programs written in Objective-C tend to be not much larger than the size of their code and that of the libraries, in contrast to Smalltalk systems where a large amount of memory was used just to open a window.

Since Objective-C is a strict superset of C, it does not treat C primitive types as first-class objects.

Objective-C uses dynamic runtime typing and because all method calls are function calls, many common performance optimizations cannot be applied to Objective-C methods.