Objective-C - Analysis of The Language

Analysis of The Language

Objective-C implementations use a thin runtime system written in C, which adds little to the size of the application. In contrast, most object-oriented systems at the time that it was created used large virtual machine runtimes. Programs written in Objective-C tend to be not much larger than the size of their code and that of the libraries (which generally do not need to be included in the software distribution), in contrast to Smalltalk systems where a large amount of memory was used just to open a window. Objective-C applications tend to be larger than similar C or C++ applications because Objective-C dynamic typing does not allow methods to be stripped or inlined. Since the programmer has such freedom to delegate, forward calls, build selectors on the fly and pass them to the runtime system, the Objective-C compiler cannot assume it's safe to remove unused methods or to inline calls.

Likewise, the language can be implemented on top of existing C compilers (in GCC, first as a preprocessor, then as a module) rather than as a new compiler. This allows Objective-C to leverage the huge existing collection of C code, libraries, tools, etc. Existing C libraries can be wrapped in Objective-C wrappers to provide an OO-style interface. In this aspect, it is similar to GObject library and Vala language, which are widely used in development of GTK applications.

All of these practical changes lowered the barrier to entry, likely the biggest problem for the widespread acceptance of Smalltalk in the 1980s.

The first versions of Objective-C did not support garbage collection. At the time this decision was a matter of some debate, and many people considered long "dead times" (when Smalltalk did collection) to render the entire system unusable. Some 3rd party implementations have added this feature (most notably GNUstep) and Apple has implemented it as of Mac OS X v10.5.

Another common criticism is that Objective-C does not have language support for namespaces. Instead, programmers are forced to add prefixes to their class names, which are traditionally shorter than namespace names and thus more prone to collisions. As of 2007, all Mac OS X classes and functions in the Cocoa programming environment are prefixed with "NS" (e.g. NSObject, NSButton) to identify them as belonging to the Mac OS X or iOS core; the "NS" derives from the names of the classes as defined during the development of NeXTstep.

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

Unlike C++, Objective-C does not support operator overloading. Also unlike C++, Objective-C allows an object to directly inherit only from one class (forbidding multiple inheritance). However, categories and protocols may be used as an alternative way to achieve the same results.

Because Objective-C uses dynamic runtime typing and because all method calls are function calls (or, in some cases, syscalls), many common performance optimizations cannot be applied to Objective-C methods (for example: inlining, constant propagation, interprocedural optimizations, and scalar replacement of aggregates). This limits the performance of Objective-C abstractions relative to similar abstractions in languages such as C++ where such optimizations are possible. However, this is an unavoidable tradeoff because such optimizations would be rendered ineffective by categories or other Objective-C runtime features that are impossible in C++.

Many programmers dislike garbage collected languages because of the runtime performance tradeoffs. Apple introduced Automatic Reference Counting (ARC) in 2011 as an alternative memory management mechanism. With ARC, the compiler inserts retain and release calls automatically into Objective-C code based on static code analysis. The automation relieves the programmer of having to write in memory management code. ARC also adds weak references to the Objective-C language.