On Thu, Nov 2, 2017 at 9:28 PM, Andrew Glynn <aglynn42@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 <black@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 aheadâ a few items, without disturbing the state of the stream. The message stream peek gives me the next item, but doesnât generalize to multiple items, So I end up writing code like this:
findSomething
| savedPosition result |
savedPosition := stream position. stream position: start. âcode 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 âexecute aroundâ method:
findSomething
^ stream unchangedDuring: [ :s |
âcode involving various manipulations of stream, including stream next"
stream position + 1 ]
Iâm 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 Iâve failed to look? - Would it be a worthwhile addition to Pharo? - What would be a good name?