2. Write-time copy technology triggered by deep and shallow copies

I. Related issues

We know that a shallow copy causes a duplicate release, causing the program to crash. While the deep copy does not have the above problem, the memory space overhead is large. So, is there a way to

Save space without causing the program to crash?

Second, write-time copy technology

Write-time copy (copy-on-write): If multiple callers require the same resource at the same time, they will collectively get the same metrics pointing to the same resource until a caller

When you try to modify it, a copy is copied to the caller.

Iii. examples

　　

2. Write-time copy technology triggered by deep and shallow copies