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has_next* methods corresponding to each next* method #3
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So the basic algorithm is the same one we use in
next()except without consuming. It seems sensible to try to export the "meat" ofnextinto a private helper function that serves both of these.The first thing
next()does is consume leading inputs. Using this forhas_nextwould break the unit test fornext_preserves_trailing_delim. Step one is to rewriteconsume_leading_delims()to return an offset instead of performing an action.- added 2 commits that reference this issue
on Feb 5, 2018 next_linedoesn't rely on next, so it doesn't follow the new rules.However, we can implement
has_next_lineas a special case: if streamhas_next, streamhas_next_line.
The design problem associated with this is that we must be able to look ahead without consuming.
As the current version makes no guarantees about tokens that do not fit in a single input buffer, we can simply examine the buffer itself. In the future, however, it will be necessary to read multiple buffers of information without consuming them.
However,
BufRead.fill_buf()will happily return the same buffer over and over again if you do notconsumein between.