Optimal way to scope mutability with Swift 6.4

Hello! First of all apologies if this topic has been discussed before. Working on a highly concurrent code base I was tempted to make all my structs completely immutable. All members are other constant structs and are declared with let all the way down. Of course this made the occasional mutation very verbose as I basically had to recreate the entire hierarchy of the value only to make a tiny change deep down within the structure. So I whipped up a little protocol to simplify the process: p...