13. Classes, Objects, and Ties

// A class has a header part traditionally named HumanCannibal.h in that case...
#import <Foundation/Foundation.h>
@interface HumanCannibal : NSObject {
    // instance variables
    NSString *stomach;
    NSString *place;
}
- (void) feed: (NSString*) input;
- (void) move: (NSString*) input;
+ (void) classOnlyMethod;
@end
// ...and an implementation part named HumanCannibal.m in that case
#import "HumanCannibal.h"
@implementation HumanCannibal
- (void) init {
    // this is the constructor. do whatever but don't forget to
    // call the parent constructor!
    [super init];
}
- (void) feed: (NSString*) input {
    stomach = input;
}
- (void) move: (NSString*) input {
    place = input;
}
- (NSString*) description {
    return [NSString stringWithFormat: @"In %@, stomach contains %@", place, stomach];
}
+ (void) classOnlyMethod {
    // do whatever
}
@end

// method calls are between square brackets
#import "HumanCannibal.h"
int main(void) {
    HumanCannibal *lector = [HumanCannibal new];
    NSLog(@"%@", lector);
    [lector feed: @"Zak"];
    [lector move: @"New York"];
    NSLog(@"%@", lector);
}
// # gcc -x objective-c -Wno-import HumanCannibal.m main.m -lobjc -lgnustep-base -fconstant-string-class=NSConstantString && ./a.out 
// 2010-07-02 13:19:47.954 a.out[8288] In (nil), stomach contains (nil)
// 2010-07-02 13:19:47.958 a.out[8288] In New York, stomach contains Zak