# doc/manual/var_t_return

Memory safety for returning by `var T` is ensured by a simple borrowing rule: If `result` does not refer to a location pointing to the heap (that is in `result = X` the `X` involves a `ptr` or `ref` access) then it has to be derived from the routine's first parameter:

    proc forward[T](x: var T): var T =
      result = x # ok, derived from the first parameter.

    proc p(param: var int): var int =
      var x: int
      # we know 'forward' provides a view into the location derived from
      # its first argument 'x'.
      result = forward(x) # Error: location is derived from `x`
                          # which is not p's first parameter and lives
                          # on the stack.

In other words, the lifetime of what `result` points to is attached to the lifetime of the first parameter and that is enough knowledge to verify memory safety at the call site.