Well, there are a few aspects to this. Mutable objects without reference-identity can cause bugs at odd times. For example, consider a Person bean with a value-based equals method: Map<Person, String> map = … Person p = new Person(); map.put(p, “Hey, there!”); p.setName(“Daniel”); map.get(p); // => null The Person instance gets “lost” in the map … Read more
It is possible… but I wish I had a more elegant solution. The trick is NOT to borrow from anchor, and therefore to juggle between two accumulators: one holding the reference to the current node the other being assigned the reference to the next node This leads me to: impl Recursive { fn back(&mut self) … Read more
It has been noted by many well respected developers such as Brian Goetz and Josh Bloch that : If an object’s hashCode() value can change based on its state, then we must be careful when using such objects as keys in hash-based collections to ensure that we don’t allow their state to change when they … Read more
What? Floats are immutable? But can’t I do x = 5.0 x += 7.0 print x # 12.0 Doesn’t that “mut” x? Well you agree strings are immutable right? But you can do the same thing. s=”foo” s += ‘bar’ print s # foobar The value of the variable changes, but it changes by changing … Read more
Structs are value types which means they are copied when they are passed around. So if you change a copy you are changing only that copy, not the original and not any other copies which might be around. If your struct is immutable then all automatic copies resulting from being passed by value will be … Read more
When you write [x]*3 you get, essentially, the list [x, x, x]. That is, a list with 3 references to the same x. When you then modify this single x it is visible via all three references to it: x = [1] * 4 l = [x] * 3 print(f”id(x): {id(x)}”) # id(x): 140560897920048 print( … Read more