It's rarely a concern in practice. Public APIs should document if a slice may or may not be modified, for example: `io.Writer` says ` Write must not modify the

It's rarely a concern in practice. Public APIs should document if a slice may or may not be modified, for example: `io.Writer` says ` Write must not modify the slice data, even temporarily`, and `bufio.Scanner.Bytes()` says `The underlying array may point to data that will be overwritten by a subsequent call to Scan`. The `append` builtin may allocate a new array and copy, or reuse the same array, but the result should almost always be assigned back to the original variable. The only time you wouldn't assign it back to the same variable is when you are carefully managing the slices yourself for some specific reason, which should never be exposed via an API.