偶然发现同事写的代码里面有两个连续的赋值，甚是懵逼，查了下链式赋值要么是oc的链式编程要么是python的链式赋值这里先记录一下。
1、给几个变量赋相同的值
一般会写
NSString *s1 = @"";
NSString *s2 = @"";
NSString *s3 = @"";
s1 = @"test1";
s2 = @"test1";
s3 = @"test1";
其实也可以这样写
NSString *s1 = @"";
NSString *s2 = @"";
NSString *s3 = @"";
s1 = s2 = s3 = @"test1";
NSLog(@"1 s1: %@, s2: %@, s3: %@", s1, s2, s3);
//或者这样：
s3 = @"test2";
s1 = s2 = s3;
NSLog(@"2 s1: %@, s2: %@, s3: %@", s1, s2, s3);
log：
2018-11-07 14:14:43.741992+0800 Test[14744:234776] 1 s1: test1, s2: test1, s3: test1
2018-11-07 14:14:43.742594+0800 Test[14744:234776] 2 s1: test2, s2: test2, s3: test2
2、如果是给对象的属性赋值呢
比如
//.h
#import <Foundation/Foundation.h>
@interface TestModel : NSObject
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) int age;
@end
//.m
#import "TestModel.h"
@implementation TestModel
- (NSString *)description {
NSString *des = [NSString stringWithFormat:@"name: %@ age: %d", self.name, self.age];
return [NSString stringWithFormat:@"<%@ %p %@>",[self class], self, des];
}
@end
//Test:
TestModel *model1 = [TestModel new];
model1.name = @"model1";
model1.age = 1;
TestModel *model2 = [TestModel new];
model2.name = @"model2";
model2.age = 2;
TestModel *model3 = [TestModel new];
model3.name = @"model3";
model3.age = 3;
NSLog(@"3 model1: %@, model2: %@, model3: %@", model1, model2, model3);
model1.name = model2.name = model3.name;
model1.age = model2.age = model3.age;
NSLog(@"4 model1: %@, model2: %@, model3: %@", model1, model2, model3);
TestModel *model = [TestModel new];
model.name = @"model";
model.age = 0;
model1 = model2 = model3 = model;
NSLog(@"5 model1: %@, model2: %@, model3: %@", model1, model2, model3);
log:
2018-11-07 14:32:41.540757+0800 Test[15362:264502] 3 model1: <TestModel 0x6000013096e0 name: model1 age: 1>, model2: <TestModel 0x600001309020 name: model2 age: 2>, model3: <TestModel 0x6000013090e0 name: model3 age: 3>
2018-11-07 14:32:41.541199+0800 Test[15362:264502] 4 model1: <TestModel 0x6000013096e0 name: model3 age: 3>, model2: <TestModel 0x600001309020 name: model3 age: 3>, model3: <TestModel 0x6000013090e0 name: model3 age: 3>
2018-11-07 14:32:41.541345+0800 Test[15362:264502] 5 model1: <TestModel 0x600001309320 name: model age: 0>, model2: <TestModel 0x600001309320 name: model age: 0>, model3: <TestModel 0x600001309320 name: model age: 0>
赋值也是正常的。
3、与python链式赋值的对比。
对比python的链式赋值会有些不同，在赋值顺序上。
在python中：
➜ ~ python
Python 2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> s = [1, 2, 3, 4, 5 , 6, 7]
>>> i = 0
>>> i = s[i] = 3
>>> i
3
>>> s
[1, 2, 3, 3, 5, 6, 7]
可以看出python是先给i赋值，然后给s[i]赋值。
在oc中：
NSMutableArray *arr1 = [@[@(0), @(2), @(3), @(4), @(5)] mutableCopy];
NSNumber *i = @(0);
i = arr1[i.intValue] = @(3);
NSLog(@"i : %@, arr : %@", i, arr1);
log
2018-11-07 14:32:41.541505+0800 Test[15362:264502] i : 3, arr : (
3,
2,
3,
4,
5
)
结果和python不同，先给arr1[i]赋值，然后才给i赋值。
赋值顺序不同可能会对赋值结果有影响。
swift中不能使用链式赋值：
image.png
