Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Wed, 02 Mar 2005 13:34:15 +0100

On Wednesday 02 March 2005 01:54, Benjamin Franksen wrote:
> An implementation based on non-contiguous storage, could take
> advantage of its storage model, and almost completely avoid copying
> (at the cost of slightly increasing the overall memory footprint).
> For instance, functional concatenation can be done in constant time
> (avoiding all allocation and copying). As long as strings are
> immutable and references are properly tracked, an implementation can
> easily share the storage between different strings (except the meta
> data). I would bet that such an implementation is in the end a lot
> more efficient than any implementation based on mutability, such as
> imposed by the dataAccess string interface.

Another advantage of functional/immutable strings is that support for 
unicode encodings is a lot easier and less error-prone. For instance, 
since a UTF-8 character may be longer than one byte, a UTF-8 encoded 
string should never be written to at an arbitrary byte index. With 
immutable strings it is much easier to maintain such invariants.

The burden, in this case, would be with string analyzing functions such 
as a generic 'split' function that turns a string into a pair 
(front,back) of strings according to some character or substring 
predicate that determines the split position. Note that such a function 
would need to traverse the string character by character anyway (to 
find teh split position). Thus, observing UTF-8 character boundaries 
would cause almost no additional overhead.

Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System