[fpc-pascal] destructor TDecompressionStream.Destroy question

[David Mears]

Michael Van Canneyt wrote:
> On Thu, 20 Sep 2007, David Mears wrote:
>
>   
>> from fpc/packages/fcl-base/src/inc/zstream.pp
>>
>> I'm not really sure why this is in the destructor for tdecompressionstream.
>>
>>   if FZRec.avail_in <> 0 then
>>     Source.Seek(-FZRec.i, soFromCurrent);
>>     
>
> To reposition the source stream on the last actually read data.
>
>  
>   
>> my tdecompressionstream  is fed by a tideadecryptstream - when
>> tdecompressionstream is freed it causes that seek in the decrypt for
>> some reason? , which isn't supported by the tdecryptionstream and it
>> throws a EIDEAError - or is there a problem with the source stream? 
>>     
>
> No, this is "normal".
>
>   
>> generally I feel that exceptions are somehow uncivilized, so avoiding
>> one so totally unnecessary  (in context, at least) would be appreciated.
>>     
>
> I'll introduce a property in TDecompressionstream: 'SourceSeekable' or so
> which can be used to control the behaviour.
>
> Another solution is to implement a long-standing idea of mine: 
>
> to introduce a property in TStream:
>   StreamCapabilities : TStreamCapabilities;
> with
>   TStreamCapability = (scSeekForward,scSeekBackward,scRead,scWrite,scSize);
>   TStreamCapabilities = set of TStreamCapability;
>
> I think I'll go for the latter one.
>
> Michael.
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>   
I like the capabilities solution.  It has the feel of "the pascal way to
do it."  There shouldn't be anything in the stream when free is called,
will research more what all is going on with that.