On 2011-01-15 16:29:47 -0500, "Steven Schveighoffer"
<[email protected]> said:
On Sat, 15 Jan 2011 15:55:48 -0500, Michel Fortin
<[email protected]> wrote:
On 2011-01-15 15:20:08 -0500, "Steven Schveighoffer"
<[email protected]> said:
I'm not suggesting we impose it, just that we make it the default. If
you want to iterate by dchar, wchar, or char, just write:
foreach (dchar c; "exposé") {}
foreach (wchar c; "exposé") {}
foreach (char c; "exposé") {}
// or
foreach (dchar c; "exposé".by!dchar()) {}
foreach (wchar c; "exposé".by!wchar()) {}
foreach (char c; "exposé".by!char()) {}
and it'll work. But the default would be a slice containing the
grapheme, because this is the right way to represent a Unicode
character.
I think this is a good idea. I previously was nervous about it, but
I'm not sure it makes a huge difference. Returning a char[] is
certainly less work than normalizing a grapheme into one or more code
points, and then returning them. All that it takes is to detect all
the code points within the grapheme. Normalization can be done if
needed, but would probably have to output another char[], since a
normalized grapheme can occupy more than one dchar.
I'm glad we agree on that now.
It's a matter of me slowly wrapping my brain around unicode and how
it's used. It seems like it's a typical committee defined standard
where there are 10 ways to do everything, I was trying to weed out the
lesser used (or so I perceived) pieces to allow a more implementable
library. It's doubly hard for me since I have limited experience with
other languages, and I've never tried to write them with a computer
(my language classes in high school were back in the days of actually
writing stuff down on paper).
Actually, I don't think Unicode was so badly designed. It's just that
nobody hat an idea of the real scope of the problem they had in hand at
first, and so they had to add a lot of things but wanted to keep things
backward-compatible. We're at Unicode 6.0 now, can you name one other
standard that evolved enough to get 6 major versions? I'm surprised
it's not worse given all that it must support.
That said, I'm sure if someone could redesign Unicode by breaking
backward-compatibility we'd have something simpler. You could probably
get rid of pre-combined characters and reduce the number of
normalization forms. But would you be able to get rid of normalization
entirely? I don't think so. Reinventing Unicode is probably not worth
it.
I'm not opposed to that on principle. I'm a little uneasy about having
so many types representing a string however. Some other raw comments:
I agree that things would be more coherent if char[], wchar[], and
dchar[] behaved like other arrays, but I can't really see a
justification for those types to be in the language if there's nothing
special about them (why not a library type?).
I would not be opposed to getting rid of those types. But I am very
opposed to char[] not being an array. If you want a string to be
something other than an array, make it have a different syntax. We
also have to consider C compatibility.
However, we are in radical-change mode then, and this is probably
pushed to D3 ;) If we can find some way to fix the situation without
invalidating TDPL, we should strive for that first IMO.
Indeed, the change would probably be too radical for D2.
I think we agree that the default type should behave as a Unicode
string, not an array of characters. I understand your opposition to
conflating arrays of char with strings, and I agree with you to a
certain extent that it could have been done better. But we can't really
change the type of string literals, can we. The only thing we can
change (I hope) at this point is how iterating on strings work.
Walter said earlier that he oppose changing foreach's default element
type to dchar for char[] and wchar[] (as Andrei did for ranges) on the
ground that it would silently break D1 compatibility. This is a valid
point in my opinion.
I think you're right when you say that not treating char[] as an array
of character breaks, to a certain extent, C compatibility. Another
valid point.
That said, I want to emphasize that iterating by grapheme, contrary to
iterating by dchar, does not break any code *silently*. The compiler
will complain loudly that you're comparing a string to a char, so
you'll have to change your code somewhere if you want things to
compile. You'll have to look at the code and decide what to do.
One more thing:
NSString in Cocoa is in essence the same thing as I'm proposing here:
as array of UTF-16 code units, but with string behaviour. It supports
by-code-unit indexing, but appending, comparing, searching for
substrings, etc. all behave correctly as a Unicode string. Again, I
agree that it's probably not the best design, but I can tell you it
works well in practice. In fact, NSString doesn't even expose the
concept of grapheme, it just uses them internally, and you're pretty
much limited to the built-in operation. I think what we have here in
concept is much better... even if it somewhat conflates code-unit
arrays and strings.
Or you could make a grapheme a string_t. ;-)
I'm a little uneasy having a range return itself as its element type.
For all intents and purposes, a grapheme is a string of one 'element',
so it could potentially be a string_t.
It does seem daunting to have so many types, but at the same time,
types convey relationships at compile time that can make coding
impossible to get wrong, or make things actually possible when having
a single type doesn't.
I'll give you an example from a previous life:
[...]
I feel that making extra types when the relationship between them is
important is worth the possible repetition of functionality. Catching
bugs during compilation is soooo much better than experiencing them
during runtime.
I can understand the utility of a separate type in your DateTime
example, but in this case I fail to see any advantage.
I mean, a grapheme is a slice of a string, can have multiple code
points (like a string), can be appended the same way as a string, can
be composed or decomposed using canonical normalization or
compatibility normalization (like a string), and should be sorted,
uppercased, and lowercased according to Unicode rules (like a string).
Basically, a grapheme is just a string that happens to contain only one
grapheme. What would a custom type do differently than a string?
Also, grapheme == "a" is easy to understand because both are strings.
But if a grapheme is a separate type, what would a grapheme literal
look like?
So in the end I don't think a grapheme needs a specific type, at least
not for general purpose text processing. If I split a string on
whitespace, do I get a range where elements are of type "word"? No,
just sliced strings.
That said, I'm much less concerned by the type used to represent a
grapheme than by the Unicode correctness. I'm not opposed to a separate
type, I just don't really see the point.
--
Michel Fortin
[email protected]
http://michelf.com/
