Swift and mutating struct

Question

There is something that I don\'t entirely understand when it comes to mutating value types in Swift.

As the \"The Swift Programming Language\" iBook states:

Answer 1

One more variant

struct MyStruct {
    var myVar = "myVar"
    let myLet = "myLet"
}

func testMutateString() {
    //given
    let myStruct = MyStruct()
    
    //Change var
    //when
    var myStructCopy = myStruct
    myStructCopy.myVar = "myVar changed 1"
    
    //then
    XCTAssert(myStructCopy.myVar == "myVar changed 1")
    
    //Change let
    //when
    withUnsafeMutableBytes(of: &myStructCopy) { bytes in
        let offset = MemoryLayout.offset(of: \MyStruct.myLet)!
        let rawPointerToValue = bytes.baseAddress! + offset
        let pointerToValue = rawPointerToValue.assumingMemoryBound(to: String.self)
        pointerToValue.pointee = "myLet changed"
    }
    
    //then
    XCTAssert(myStructCopy.myLet == "myLet changed")
}

[Swift types]