code: func WithStringAndArg(b []byte, arg interface{}, fn StringAndArgFn) {
  	fn(String(b), arg)
  }
docs: // WithStringAndArg converts a byte slice to a string with zero heap memory
  // allocations, and calls a function to process the string with one argument.
  // It is the caller's responsibility to make sure it holds no reference to the
  // string after the function returns.