Swift Object ModelLesson 35Free preview

Value Semantics & COW

This lesson is part of Swift · All levels

Summary

This lesson is a study of the concept of Value Semantics and Copy-on-Write (COW) optimization in Swift. Value semantics guarantees that each variable has an independent copy of the data so that no wild mutation side effects occur. To prevent memory loss when copying large data structures like Array and String, Swift implemented COW.

Key points

Value semantics ensures that modifications to one variable will never change another variable
Built-in data structures (Array, String, Dictionary, Set) apply Copy-on-Write (COW) to the data
Data is only actually copied into the physical memory when there is a mutation.
The 'isKnownUniquelyReferenced()' function is used to create the COW mechanism on a custom struct type

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