Swift value type memory management

ValueTypePlayground.swift

import Cocoa

func address(of object: UnsafeRawPointer) -> String {
    let addr = Int(bitPattern: object)
    return String(format: "%p", addr)
}

struct Foo {
    public var baz: String
}

struct Bar {
    public private(set) var baz: String
    
    mutating func updateBaz(with text: String) {
        baz = text
    }
}

var foo = Foo(baz: "yankee")
print("Foo holds \(foo.baz)", address(of: &foo))
foo.baz = "doodle"
print("Foo holds \(foo.baz)", address(of: &foo))

var bar = Bar(baz: "sporty")
print("Bar holds \(bar.baz)", address(of: &bar))
bar.updateBaz(with: "spice")
print("Bar holds \(bar.baz)", address(of: &bar))

This Playground demonstrates that a setter is implicitly mutating. You will not get a copy of a struct (value type - copy on write) when you directly update one of its properties (Foo). There is no need for a mutating method to do so (Bar). When you run, the output will be something like:

Foo holds yankee 0x10fcb9430
Foo holds doodle 0x10fcb9430
Bar holds sporty 0x10fcb9440
Bar holds spice 0x10fcb9440

Both Foo as well as Bar have the same address space after mutation.