On Thu, 02 Dec 2010 02:09:51 -0500, Lars T. Kyllingstad
<[email protected]> wrote:
On Wed, 01 Dec 2010 16:44:42 -0500, Steven Schveighoffer wrote:
On Tue, 30 Nov 2010 18:34:11 -0500, Lars T. Kyllingstad
<[email protected]> wrote:
On Tue, 30 Nov 2010 13:52:20 -0500, Steven Schveighoffer wrote:
On Tue, 30 Nov 2010 13:34:50 -0500, Jonathan M Davis
<[email protected]> wrote:
[...]
4. Indexing is no longer O(1), which violates the guarantees of the
index operator.
Indexing is still O(1).
5. Slicing (other than a full slice) is no longer O(1), which
violates the
guarantees of the slicing operator.
Slicing is still O(1).
[...]
It feels extremely weird that the indices refer to code units and not
code points. If I write
auto str = mystring("hæ?");
writeln(str[1], " ", str[2]);
I expect it to print "æ ?", not "æ æ" like it does now.
I don't think it's possible to do that with any implementation without
making indexing not O(1). This just isn't possible, unless you want to
use dchar[].
But your point is well taken. I think what I'm going to do is throw an
exception when accessing an invalid index. While also surprising, it
doesn't result in "extra data". I feel it's probably very rare to just
access hard-coded indexes like that unless you are sure of the data in
the string. Or to use a for-loop to access characters, etc.
As soon as you add opIndex(), your interface becomes that of a random-
access range, something which narrow strings are not. In fact, the
distinction between random access and bidirectional range access for
strings is in many ways the reason we're having this discussion.
How about dropping opIndex() for UTF-8 and UTF-16 strings, and instead
adding a characterAt(i) function that retrieves the i'th code point, and
which is not required to be O(1)? Then, if someone wants O(1) indexing
they are forced to use string_t!dchar or just plain ol' arrays, both of
which have clear, predictable indexing semantics.
Then substring (slicing) becomes an O(n) operation. It just doesn't work
well. It seems to be awkward at first thought, but the more I think about
it, the more I think it's right. When do you ever depend on specific
indexes in a string being valid, or to be incrementing always by 1?
I think it's great that you're doing this, by the way! I haven't made up
my mind yet about whether I want char[] or a separate string type, but it
is great to have an actual implementation of the latter at hand when
debating it.
Thanks :)
-Steve
