Swift Value Semantics & COW
Value Semantics & COW
Prefer value semantics for predictability.
Swift collections use Copy-on-Write (COW) to keep copies cheap until mutation.
Syntax
var a = [1,2,3]
Arrays, sets, and dictionaries use value semantics.
Copy-on-Write
Swift collections use Copy-on-Write (COW) to keep copies cheap until mutation.
Example
var a = [1,2,3]
var b = a // shares storage
b.append(4) // triggers copy for b only
print(a) // [1,2,3]
print(b) // [1,2,3,4]This example shows that arrays use value semantics and COW.
In the example above, b shares storage with a, but when b.append(4) is called, a copy is made for b only.
