[boost] IOstreams: Why are mapped_file devices not seekable?

From: Schalk_Cronje_at_[hidden]
Date: 2007-08-17 06:03:10

In both of the implementations of mapped_file_source and
mapped_file_sink, the devices are not seekable (whereas
basic_array_source and basic_array_sink are). 

I am wondering whether there is a rationale for this, or whether it was
simply an oversight in development. Since mapped_files are still
contiguous piece of memory I see no reason why they should not be
seekable.

On a side note, should a direct_tag not imply ssekable_device_tag i.e.,

        struct direct_tag : seekable_device_tag {};