The more you add, the more you'll have to remove

2013/12/10 Damien Cassou <damien.cassou@gmail.com>

On Dec 5, 2013 10:50 PM, "Max Leske" <maxleske@gmail.com> wrote:
>
> There are several different approaches in different places:
>
> - FileStream reads strings by default. #binary and #ascii switch between formats. File streams use an internal buffer which is either a String (default) or a ByteArray. It�s even possible to switch between binary and ascii midstream without losing information (if done right) because it only affects the buffer.
> - ReadStream and WriteStream cannot change their format. Their behavior is determined by the underlying collection. Forcing conversions (e.g. by #asString) can lead to loss of information
> - RWBinaryOrTextStream (and other subclasses of ReadWriteStream) also support the #binary #ascii method of switching format. Default is #ascii
> - SocketStream uses the same #binary / #ascii mechanism. Default is #ascii
> - ZnLimitedReadStream uses the same #binary / #ascii mechanism. Default is #binary (implicit); depends on the underlying stream
>
> I think the pattern to follow is clear: ReadStream and WriteStream should allow switching format with #ascii and #binary, default should be #ascii. However, I suspect there�s a reason that these classes don�t support switching, namely that switching makes the implementation more complicated and also slower because more checks need to be made.
>
> The easiest solution I see would be to implement something like this:
>
> ReadStream>>next
> ^ self isBinary
> ifTrue: [ self basicNext asCharacter ]
> ifFalse: [ self basicNext ]
>
> However, #next et al. are implemented in a plugin and the primitive method looks like this:
>
> ReadStream>>next
> <primitive: 65> 
> position >= readLimit 
> ifTrue: [^nil] 
> ifFalse: [^collection at: (position := position + 1)]
>
> This means the collection instance variable has to hold either a binary or a string collection.
>
> I�ve found a solution which would work and I�ve whipped up a working way (there�s space for improvement�):
>
> ReadStream>>binary
> collection isString ifFalse: [ ^ self ].
> collection := (ByteArray new: collection size) copyReplaceFrom: 1 to: collection size with: collection
>
> ReadStrem>>ascii
> collection isString ifTrue: [ ^ self ].
> collection := (String new: collection size) copyReplaceFrom: 1 to: collection size with: collection
>
> @Damien
> opposed to what I wrote earlier, #asString does *not* destroy non-printable characters. Instead, every byte (from 0 to 255) is encoded as a character and thus the string can be converted back to a ByteArray *without* loss of information. Sorry about that.

Thank you very much for your analysis. I'm a bit reluctant to change ReadStream now, but I could be ok with enough unit tests.
Another potential solution: What about adding a #binaryReadStream method to the memory file system as a workaround before the introduction of xstreams ?

> With this change in place the 12259 would become obsolete.
>
> Please let me know what you think. This is a pretty big change that might have a lot of consequences in the image.
>
> Cheers,
> Max
>
> On 04.12.2013, at 13:14, Max Leske <maxleske@gmail.com> wrote:
>
>> Let me see what I can come up with.
>>
>>
>> On 03.12.2013, at 19:36, Damien Cassou <damien.cassou@gmail.com> wrote:
>>
>>> Thanks Max for the report. Do you have an idea on how we could solve the problem ? The previous behaviour was not acceptable either because the streams that came out of a memory filesystem were the only ones with binary content
>>>
>>> On Dec 3, 2013 5:35 PM, "Max Leske" <maxleske@gmail.com> wrote:
>>>>
>>>> Damien, Marcus
>>>>
>>>> this change breaks a lot of things in FileSystem-Git. I don�t disagree with the idea that reading characters should be default (one could argue about it�) but your change makes it IMPOSSIBLE to read bytes because unprintable characters are discarded! So if my ByteArray is a NULL terminated string, for instance, I can not check for the NULL termination anymore.
>>>>
>>>> Cheers,
>>>> Max
>>
>>
>