114140 - need clearer API for writing to strings

Status: RESOLVED INCOMPLETE

(Core :: XPCOM, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

This is partly a spin-off of some of the early discussion in bug 104663.

|SetLength| and |SetCapacity| are rather ugly members of the string API, and
they do multiple things that aren't clear from their names.  It's also not clear
what the rules for using writing iterators are.  We need to address these issues.

A possible public API to replace these functions would be:
 * |Truncate| - already exists, and could replace most (?) calls to |SetLength|.
 * |EnsureCapacity| - if one wants to use writing iterators to write a length
longer than the current one or ensure capacity for an append.  (Alternately,
this could be required for *all* writes to a string and we wouldn't override
GetWritableFragment on sharable strings -- which we need to do -- to ensure a
unique buffer.)
 * |ReleaseStorage| - do we even need this?  See
http://bugzilla.mozilla.org/show_bug.cgi?id=104663#c0
 * |DidWrite(nsWritingIterator& aIter)| - tell a string that one has written a
specific amount (perhaps smaller than the capacity ensured by |EnsureCapacity|),
and allow it to null-terminate itself if it is flat.

See http://lxr.mozilla.org/seamonkey/source/string/src/nsSharableString.cpp#40
for some additional comments.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Note that if |EnsureCapacity| were required for all writes, it would need to be
called something else, like |WillWrite|.

Comment 2

[Scott Collins]

giving up ancient string bugs to the new string owner.  jag, you'll want to sort
through these and see which ones still apply and go with or against the
direction in which you intend strings evolve