Perhaps #keepStateWhile or something similar might be better than #unchangedDuring ?

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Sent: Thursday, November 2, 2017 5:00 AM

To: Any question about pharo is welcome

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?