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mikeash/runtime-class.m

Created November 22, 2013 16:46
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  1. mikeash created this gist Nov 22, 2013.
    80 changes: 80 additions & 0 deletions runtime-class.m
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,80 @@
    // clang -fobjc-arc -framework Foundation runtime-class.m

    #import <Foundation/Foundation.h>

    #import <objc/runtime.h>


    @interface Person : NSObject

    - (id)initWithFirstName: (NSString *)firstName lastName: (NSString *)lastName age: (NSUInteger)age;

    @property (readonly) NSString *firstName;
    @property (readonly) NSString *lastName;
    @property (readonly) NSUInteger age;

    @end


    int main(int argc, char **argv)
    {
    @autoreleasepool
    {
    Class c = objc_allocateClassPair([NSObject class], "Person", 0);
    class_addIvar(c, "firstName", sizeof(id), log2(sizeof(id)), @encode(id));
    class_addIvar(c, "lastName", sizeof(id), log2(sizeof(id)), @encode(id));
    class_addIvar(c, "age", sizeof(NSUInteger), log2(sizeof(NSUInteger)), @encode(NSUInteger));

    Ivar firstNameIvar = class_getInstanceVariable(c, "firstName");
    Ivar lastNameIvar = class_getInstanceVariable(c, "lastName");
    ptrdiff_t ageOffset = ivar_getOffset(class_getInstanceVariable(c, "age"));

    IMP initIMP = imp_implementationWithBlock(^(id self, NSString *firstName, NSString *lastName, NSUInteger age) {
    object_setIvar(self, firstNameIvar, firstName);
    object_setIvar(self, lastNameIvar, lastName);

    char *agePtr = ((char *)(__bridge void *)self) + ageOffset;
    memcpy(agePtr, &age, sizeof(age));

    return self;
    });
    const char *initTypes = [[NSString stringWithFormat: @"%s%s%s%s%s%s", @encode(id), @encode(id), @encode(SEL), @encode(id), @encode(id), @encode(NSUInteger)] UTF8String];
    class_addMethod(c, @selector(initWithFirstName:lastName:age:), initIMP, initTypes);

    const char *objectGetterTypes = [[NSString stringWithFormat: @"%s%s%s", @encode(id), @encode(id), @encode(SEL)] UTF8String];

    IMP descriptionIMP = imp_implementationWithBlock(^(id self) {
    return [NSString stringWithFormat: @"<%@ %p: %@ %@ age %zd>", [self class], self, [self firstName], [self lastName], [self age]];
    });
    class_addMethod(c, @selector(description), descriptionIMP, objectGetterTypes);

    IMP firstNameIMP = imp_implementationWithBlock(^(id self) {
    return object_getIvar(self, firstNameIvar);
    });
    class_addMethod(c, @selector(firstName), firstNameIMP, objectGetterTypes);

    IMP lastNameIMP = imp_implementationWithBlock(^(id self) {
    return object_getIvar(self, lastNameIvar);
    });
    class_addMethod(c, @selector(lastName), lastNameIMP, objectGetterTypes);

    IMP ageIMP = imp_implementationWithBlock(^(id self) {
    char *agePtr = ((char *)(__bridge void *)self) + ageOffset;
    NSUInteger age;
    memcpy(&age, agePtr, sizeof(age));
    return age;
    });
    const char *ageTypes = [[NSString stringWithFormat: @"%s%s%s", @encode(NSUInteger), @encode(id), @encode(SEL)] UTF8String];
    class_addMethod(c, @selector(age), ageIMP, ageTypes);

    objc_registerClassPair(c);

    Class PersonC = NSClassFromString(@"Person");
    Person *alex = [[PersonC alloc] initWithFirstName: @"Alex" lastName: @"Trebek" age: 29];
    Person *sean = [[PersonC alloc] initWithFirstName: @"Sean" lastName: @"Connery" age: 42];

    NSArray *people = @[ alex, sean ];

    NSLog(@"%@", people);
    }
    }