On Thu, Nov 2, 2017 at 9:28 PM, Andrew Glynn <aglyn...@gmail.com> wrote:
> Perhaps #keepStateWhile or something similar might be better than > #unchangedDuring ? > Something like "keepState" was also my first impression, but "During" seems to be the convention for restoring things after a code block completes. Are there methods breaking that convention? cheers -ben *From: *Prof. Andrew P. Black <bl...@cs.pdx.edu> > *Sent: *Thursday, November 2, 2017 5:00 AM > *To: *Any question about pharo is welcome <pharo-users@lists.pharo.org> > *Subject: *[Pharo-users] Peeking at a stream > > > > I sometimes find, when working with a stream, that I need to "peek ahead” > a few items, without disturbing the state of the stream. The message stream > peek gives me the next item, but doesn’t generalize to multiple items, So > I end up writing code like this: > > > > findSomething > > | savedPosition result | > > savedPosition := stream position. > stream position: start. > “code involving various manipulations of stream, including > stream next" > result := stream position + 1. > stream position: savedPosition. > > ^ result > > > > This code involves at least two temps, is not very easy to read, and risks > not resetting the stream properly if I do a return. > > > > It seems to me that a better solution would be what Kent Beck calls an > “execute around” method: > > > > findSomething > > ^ stream unchangedDuring: [ :s | > > “code involving various manipulations of > stream, including stream next" > > stream position + 1 ] > > > > I’m not sure that I like the name #unchangedDuring:; perhaps you can think > of a better one? > > > > The implementation of this would be > > > > PositionableStream >> #unchangedDuring: aBlock > > "execute aBlock with self as argument. Ensure > that when this method returns, > > I still have my current state." > > > > | savedPosition | > > savedPosition := self position. > ^ [ aBlock value: self ] ensure: [ self > position: savedPosition ] > > > > or perhaps > > > > PositionableStream >> #unchangedDuring: aBlock > "execute aBlock with self as argument. Ensure > that when this method returns, > > I still have my current state." > > > ^ [ aBlock value: self copy ] > > > > which might be better in the case that the stream is a file stream and > aBlock causes the buffer to be refreshed from the disk. > > > > - Do other Smalltalks have a method like this? > - Does it already exist in Pharo, somewhere that I’ve failed to look? > - Would it be a worthwhile addition to Pharo? > - What would be a good name? > > > > > > > > >
