Deep copy and shallow copy of iOS development (mutablecopy and copy)

Basic concepts and usage of deep-shade copies

Basic concepts

　　Shallow copy paper Copy the object itself, the object's properties, the contained object does not copy

A deep copy duplicates both the object itself and the object's properties.

The class that supports replication in the Foundation framework is a shallow copy by default.

Copy and Mutabelcopy

1. An object can create a copy of an object using the copy and Mutabelcopy methods
2. Copy-you need to implement the Nscoppying protocol first, creating immutable replicas (such as NSString, Nsarray, Nsdictionary)
3. Mutabelcopy-You need to implement the Nsmutabelcopying protocol first, creating a mutable copy (such as nsmutabelstring, Nsmutabelarray, Nsmutabeldictionary)
4. Deep copy: A copy of the content, the source object and the copy point to a different two objects. The source object reference counter is unchanged, and the replica counter is set to 1
5. Shallow copy: pointer copy, source object and copy point to the same object. Object reference counter +1 is actually equivalent to doing a retain operation
6. Only immutable objects Create immutable replicas (copy) is shallow copy, others are deep copy

Example: A custom copy of an object

The object has a copy attribute, which implements the Nscopying, nsmutabelcopying protocol to implement the copywithzone of the Protocol: Methods and Mutabelcopywithzone: Methods

Code:

Different implementations of the shades of a copy; code examples

The difference between a Objective-c object's dark copy is that you have different implementations of Copywithzone

A summary of the depth of the copy and the retain

The relationship between copy, Mutabelcopy, and retain

• Foundation replicable object, when we copy an immutable object, his role is equivalent to retain (Cocoa do memory optimization)
• When we use Mutabelcopy, the copy is mutable regardless of the source master, and it implements a true copy
• When we copy a mutable object, the replica object is immutable, and it also implements a true copy

Some common replication cases for Foundation

Deep copy and shallow copy of iOS development (mutablecopy and copy)