isOpen returns true if the ByLineSource instance is open for reading, false
otherwise.
"Open" in this context is whether the ByLineSource object is currently "open".
The underlying input source backing it does not necessarily have the same
state. The ByLineSource instance is "open" if is the front element of the
ByLineSourceRange that created it.
The underlying input source object follows the same open/close state as makes
sense. In particular, real files are closed when the ByLineSource object is
closed. The exception is standard input, which is never actually closed.
isOpen returns true if the ByLineSource instance is open for reading, false otherwise.
"Open" in this context is whether the ByLineSource object is currently "open". The underlying input source backing it does not necessarily have the same state. The ByLineSource instance is "open" if is the front element of the ByLineSourceRange that created it.
The underlying input source object follows the same open/close state as makes sense. In particular, real files are closed when the ByLineSource object is closed. The exception is standard input, which is never actually closed.