Поддерживает ли механизм copy-on-write оптимизацию при работе со строками?

Yes, the copy-on-write (COW) mechanism optimizes string handling in some languages and platforms, including iOS (Objective-C and Swift).

In iOS, strings (NSString, Swift String) are implemented so that when a string is copied, a new copy of the data is not actually created; instead, a new reference to the same data is made. Actual copying occurs only when an attempt is made to modify the string — at which point a separate instance with the changes is created.

This allows for efficient memory usage and improves performance when working with immutable strings.

Example in Swift:

var str1 = "Hello"
var str2 = str1 // str2 and str1 point to the same data

str2 += " world" // now str2 creates a copy and is modified, str1 remains unchanged

Thus, copy-on-write helps avoid unnecessary copying until it is truly needed.