On 8/31/2011 5:58 PM, Neil Hodgson wrote:
Glenn Linderman:
That said, regexp, or some sort of cursor on a string, might be a workable
solution. Will it have adequate performance? Perhaps, at least for some
applications. Will it be as conceptually simple as indexing an array of
graphemes? No. Will it ever reach the efficiency of indexing an array of
graphemes? No. Does that matter? Depends on the application.
Using an iterator for cluster access is a common technique
currently. For example, with the Pango text layout and drawing
library, you may create a PangoLayoutIter over a text layout object
(which contains a UTF-8 string along with formatting information) and
iterate by clusters by calling pango_layout_iter_next_cluster. Direct
access to clusters by index is not as useful in this domain as access
by pixel positions - for example to examine the portion of a layout
visible in a window.
http://developer.gnome.org/pango/stable/pango-Layout-Objects.html#pango-layout-get-iter
In this API, 'index' is used to refer to a byte index into UTF-8,
not a character or cluster index.
I agree that different applications may have different needs for
different types of indexes to various starting points in a large
string. Where a custom index is required, a standard index may not be
needed.
One of the benefits of iterator access to text is that many
different iterators can be built without burdening the implementation
object with extra memory costs as would be likely with techniques that
build indexes into the representation.
How many different iterators into the same text would be concurrently
needed by an application? And why? Seems like if it is dealing with
text at the level of grapheme clusters, it needs that type of iterator.
Of course, if it does I/O it needs codec access, but that is by nature
sequential from the starting point to the end point.
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