copy 和 mutableCopy 如何应用于 NSArray 和 NSMutableArray? [英] How do copy and mutableCopy apply to NSArray and NSMutableArray?

问题描述

copy 和 mutableCopy 在 NSArray 或 NSMutableArray 上使用时有什么区别?

What is the difference between copy and mutableCopy when used on either an NSArray or an NSMutableArray?

这是我的理解；正确吗?

This is my understanding; is it correct?

// ** NSArray **
NSArray *myArray_imu = [NSArray  arrayWithObjects:@"abc", @"def", nil];

// No copy, increments retain count, result is immutable
NSArray *myArray_imuCopy = [myArray_imu copy];

// Copys object, result is mutable 
NSArray *myArray_imuMuta = [myArray_imu mutableCopy];

// Both must be released later

<小时>

// ** NSMutableArray **
NSMutableArray *myArray_mut = [NSMutableArray arrayWithObjects:@"A", @"B", nil];

// Copys object, result is immutable
NSMutableArray *myArray_mutCopy = [myArray_mut copy];

// Copys object, result is mutable
NSMutableArray *myArray_mutMuta = [myArray_mut mutableCopy];

// Both must be released later

推荐答案

copy 和 mutableCopy 定义在不同的协议(NSCopying 和 NSMutableCopying，分别)和 NSArray 符合两者.mutableCopy 是为 NSArray(不仅仅是 NSMutableArray)定义的，它允许你制作一个原始不可变数组的可变副本:

copy and mutableCopy are defined in different protocols (NSCopying and NSMutableCopying, respectively), and NSArray conforms to both. mutableCopy is defined for NSArray (not just NSMutableArray) and allows you to make a mutable copy of an originally immutable array:

// create an immutable array
NSArray *arr = [NSArray arrayWithObjects: @"one", @"two", @"three", nil ];

// create a mutable copy, and mutate it
NSMutableArray *mut = [arr mutableCopy];
[mut removeObject: @"one"];

总结:

• 您可以依赖 mutableCopy 的结果是可变的，而不管原始类型如何.对于数组，结果应该是 NSMutableArray.
• 你不能依赖于copy的结果是可变的！copyNSMutableArray 可能返回一个 NSMutableArray，因为这是原始类，但是 copycode>ing 任何任意 NSArray 实例都不会.

• you can depend on the result of mutableCopy to be mutable, regardless of the original type. In the case of arrays, the result should be an NSMutableArray.
• you cannot depend on the result of copy to be mutable! copying an NSMutableArray may return an NSMutableArray, since that's the original class, but copying any arbitrary NSArray instance would not.

根据 Mark Bessey 的回答重新阅读您的原始代码.当您创建阵列的副本时，当然您仍然可以修改原始阵列，无论您对副本进行什么操作.copy vs mutableCopy 影响新数组是否可变.

re-read your original code in light of Mark Bessey's answer. When you create a copy of your array, of course you can still modify the original regardless of what you do with the copy. copy vs mutableCopy affects whether the new array is mutable.

编辑 2: 修正了我的(错误)假设，即 NSMutableArray -copy 将返回一个 NSMutableArray.

Edit 2: Fixed my (false) assumption that NSMutableArray -copy would return an NSMutableArray.

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