Answers

1. String is a fixed-size reference stored in the stack that points to string-type data on the heap. str is an immutable sequence of bytes stored somewhere in memory. Because the size of str is unknown, it can only be handled by a &str pointer.
2. Since we do not know the size of the string slice at compile time, we cannot allocate the correct amount of memory for it. Strings, on the other hand, have a fixed-size reference stored on the stack that points to the string slice on the heap. Because we know this fixed size of the string reference, we can allocate the correct amount of memory and pass it through to a function.
3. We use the HashMap’s get function. However, we must remember that the get function merely returns an Option struct. If we are confident that there is something there or we want the program to crash if nothing is found, we can directly unwrap it. However, if we don’t want that, we can use a match statement and handle the Some and None...