01 — the bracket message
A message send in brackets: receiver, selector, arguments. Verbose, unmistakable.
NSString *s =
[@"Mac" stringByAppendingString:@"intosh"];§ 02 — Eras · 1984
Objective-C
Smalltalk messages bolted onto C — Apple’s thirty-year accent
Left: era context, features, and the 101 hello. Right: 3 core concepts, 3 deeper 201 lessons, the factorial specimen, and where Objective-C lives today — each column scrolls on its own.
The problem it solves
Objects were proven, but C owned systems software. Objective-C brought messaging to C with a layer thin enough to ship.
The problem it carries
Verbose brackets, two type systems in one file, and (for most of its life) memory management by hand.
Key features
- the message
- Bracket syntax for any message; the selector is a first-class string you can build at run time.
- reference counting
- Ownership by retain and release — manual before ARC, automatic after.
- categories
- Extend any class, including ones you did not write and cannot change.
- a dynamic runtime
- Message forwarding, runtime introspection and key-value observing underneath it all.
101 — hello, world
Session one is the smallest program that still counts as speaking Objective-C: what every tutorial prints first, in the dialect that mattered when the language arrived (1984).
#import <Foundation/Foundation.h>
int main(void) {
NSLog(@"Hello, world");
return 0;
}101First contact — hello world and 3 ideas that define how Objective-C reads. 201 — 3 lessons on mechanisms you meet after the factorial specimen: the sharp edges practitioners actually use.
101 — core concepts
3 fragments, each naming a habit of mind in Objective-C. Read the note, then the code — together they are the 101 in one sitting.
02 — interface & implementation
The @-directives layer objects over plain C — two languages, one file.
@interface Ship : NSObject
@property (copy) NSString *name;
- (void)sail;
@end03 — categories
Open any class and add methods — for better and for worse.
@interface NSString (Nautical)
- (BOOL)isShipName;
@end201 — going deeper
The 201 assumes you have read the 101 and the specimen. Each lesson is one mechanism — what it is for, how it looks in code, and the trap or payoff that makes Objective-C distinctive at scale.
blocks
Blocks are closures with captured state — the way to pass behaviour to asynchronous APIs without the ceremony of a target-selector pair.
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger i, BOOL *stop) {
NSLog(@"%@", obj);
}];the runtime
Objective-C’s runtime is an object graph you can edit at run time: swizzling a method, adding a class, or forwarding a message no one implements.
Method m = class_getInstanceMethod([Foo class],
@selector(bar));
method_exchangeImplementations(m, other);nullability and lightweight generics
Nullability annotations and parameterized types are compile-time only — they erase to plain objects, keeping the runtime compatible.
- (nullable NSArray<NSString *> *)namesFor:(nonnull NSString *)key;The specimen — factorial
The bracket message: Smalltalk’s words bolted onto C’s bones — verbose, unmistakable, and the sound of Apple software for thirty years.
NSString *s =
[@"Mac" stringByAppendingString: @"intosh"];Run it today
runclang -framework Foundation fact.m -o fact && ./fact
Where it is now
Legacy Apple platforms; Swift interoperates with it to this day.