On 07/02/2014 12:34 AM, Sam Tobin-Hochstadt wrote:
> Racket stores strings as arrays of 4-byte characters.

On 07/02/2014 07:06 AM, Michael Montague wrote:
> Foment uses 4 bytes to store each character in a string.

The follow-up question is: When you have a Scheme reference
to a string, presumably that is a pointer to a string object header
containing at least a size and maybe some kind of typecode.  The
actual data characters can be stored right next to the header (inlined),
or the header can have a pointer to a separate array of data characters
(indirected).  The latter makes it easy to resize the array by re-allocating
it; doing it inlined makes resizing difficult.

I would argue that the ability to resize a mutable string is so important
that it justifies the slight overhead of indirection.  (Indirection may
also be easier to implement, depending on how your memory allocation works.)

In other words: Supporting string-replace! has no extra overheads beyond
requiring an "indirect" representation.  The latter is forced anyway if
you support mutability and full Unicode, unless you use 3- or 4-byte characters.
Even if you do use 3- or 4-byte characters, indirection is worth it, because
mutable fixed-size strings is an essentially-useless feature.
--
	--Per Bothner
per@bothner.com   http://per.bothner.com/

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