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?