Objective-C
Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It was the primary language used by Apple for macOS and iOS development before the introduction of Swift, and it remains in use for maintaining legacy codebases. The language is known for its dynamic runtime and extensive use in the Cocoa and Cocoa Touch frameworks.
Developers should learn Objective-C primarily for maintaining and updating existing macOS and iOS applications that were built before Swift became dominant, as many legacy Apple projects still rely on it. It is also useful for understanding the foundations of Apple's development ecosystem, such as the Cocoa frameworks and dynamic runtime features. Knowledge of Objective-C can be beneficial when working with mixed codebases that include both Objective-C and Swift components.