On Sat, 15 Jan 2011 17:45:37 -0500, Michel Fortin
<[email protected]> wrote:
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.
I didn't read the standard, all I understand about unicode is from this NG
;) What I meant was the ability to do things more than one way seems like
a committee-designed standard. Usually with one of those, you have one
party who "absolutely needs" one way of doing things (most likely because
all their code is based on it), and other parties who want it a different
way. When compromises occur, the end result is, you have a standard
that's unnecessarily difficult to implement.
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.
I was hoping to change string literal types. If we don't do that, we have
a half-ass solution. I don't think it's going to be impossible, because
string, wstring, dstring are all aliases.
In fact, with my current proposed type, this already works:
mystring s = "hello";
But this doesn't:
auto s = "hello"; // still typed as immutable(char)[]
This isn't so bad, just require one to specify the type, right? Well, it
fails miserably here:
foo(mystring s) {...}
foo("hello"); // fails to match.
In order to have a string type, string literals have to be typed as that
type.
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.
Changing iteration and not indexing is not going to fix the mess we have
right now.
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.
But is NSString typed the *exact same* as an array, or is it a wrapper for
an array? Looking at the docs, it appears it is not.
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?
A grapheme type would not be a range, it would be an element of the string
range. You could not append to it (otherwise, that makes it into a
string).
In all other respects, it should act similar to a string (as you say,
printing, upper-casing, comparison, etc.)
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?
A grapheme should be comparable to a string literal. It should be
assignable to a string literal. The drawback is we would need a runtime
check to ensure the string literal was actually one grapheme. Some
compiler help in this regard would be useful, but I'm not sure how the
mechanics would work (you couldn't exactly type a literal differently
based on its contents). Another possibility is to come up with a
different syntax to denote grapheme literals.
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.
It is not clear that using a separate type is the "right answer." It may
be that an element of a string should be a string. This does work in
other languages that don't have a concept of a character. An extra type
however, allows us to have more concrete positions to work with.
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.
I will try to explain better by making an actual candidate type.
-Steve
