iOS中instancetype和id的区别

1、instancetype

1. instancetype不可以跟id那样，作为参数进行传递，只可以作为方法的返回值
2. 当一个类返回相同类的实例时可以使用instancetype

2、id

1. 不在描述

3、代码反馈
    Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject

+ (instancetype)personInstancetype;
+ (id)personID;

- (void)does;
@end

    Person.m

#import "Person.h"

@implementation Person

+ (instancetype)personInstancetype
{
    return [[self alloc] init];
}
+ (id)personID
{
    return [[self alloc] init];
}
- (void)does
{
    NSLog(@"person does");
}
@end

    
    Man.h

#import "Person.h"

@interface Man : Person

- (void)doIt;
@end

    Man.m

#import "Man.h"

@implementation Man

- (void)doIt
{
    NSLog(@"man do it ");
}
@end

    调用执行过程如下：
    main.m

#import <UIKit/UIKit.h>

#import "AppDelegate.h"
#import "Person.h"
#import "Man.h"

int main(int argc, char *argv[])
{
    @autoreleasepool {
        [[Person personID] does];
        [[Person personID] doIt];

        [[Person personInstancetype] doIt];
        [[Person personInstancetype] does];

        [[Man personInstancetype] doIt];
        [[Man personInstancetype] does];

        [[Man personID] does];
        [[Man personID] doIt];

        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

      在13行会有编译器提示，如下：

/Users/...../Demo/Demo/main.m:21:38: No visible @interface for 'Person' declares the selector 'doIt'