study_objc4/objc4-779.1/test/accessors.m

// TEST_CFLAGS -framework Foundation

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/objc-abi.h>
#include "test.h"

@interface Test : NSObject {
    NSString *_value;
    // _object is at the last optimized property offset
    id _object __attribute__((aligned(64)));
}
@property(readonly) Class cls;
@property(copy) NSString *value;
@property(assign) id object;
@end

typedef struct {  
    void *isa;
    void *_value;
    // _object is at the last optimized property offset
    void *_object __attribute__((aligned(64)));
} TestDefs;

@implementation Test

// Question:  why can't this code be automatically generated?

#if !__has_feature(objc_arc)
- (void)dealloc {
    self.value = nil;
    self.object = nil;
    [super dealloc];
}
#endif

- (Class)cls { return objc_getProperty(self, _cmd, 0, YES); }

- (NSString*)value { return (NSString*) objc_getProperty(self, _cmd, offsetof(TestDefs, _value), YES); }
- (void)setValue:(NSString*)inValue { objc_setProperty(self, _cmd, offsetof(TestDefs, _value), inValue, YES, YES); }

- (id)object { return objc_getProperty(self, _cmd, offsetof(TestDefs, _object), YES); }
- (void)setObject:(id)inObject { objc_setProperty(self, _cmd, offsetof(TestDefs, _object), inObject, YES, NO); }

- (NSString *)description {
    return [NSString stringWithFormat:@"value = %@, object = %@", self.value, self.object];
}

@end

int main() {
    PUSH_POOL {
    
        NSMutableString *value = [NSMutableString stringWithUTF8String:"test"];
        id object = [NSNumber numberWithInt:11];
        Test *t = AUTORELEASE([Test new]);
        t.value = value;
        [value setString:@"yuck"];      // mutate the string.
        testassert(t.value != value);   // must copy, since it was mutable.
        testassert([t.value isEqualToString:@"test"]);
        
        Class testClass = [Test class];
        Class cls = t.cls;
        testassert(testClass == cls);
        cls = t.cls;
        testassert(testClass == cls);
        
        t.object = object;
        t.object = object;
        
        // NSLog(@"t.object = %@, t.value = %@", t.object, t.value);
        // NSLog(@"t.object = %@, t.value = %@", t.object, t.value); // second call will optimized getters.
        
    } POP_POOL;

    succeed(__FILE__);

    return 0;
}