On 01/01/2012 02:34 AM, Chad J wrote:
On 12/31/2011 02:02 PM, Timon Gehr wrote:
On 12/31/2011 07:22 PM, Chad J wrote:
On 12/30/2011 02:55 PM, Timon Gehr wrote:
On 12/30/2011 08:33 PM, Joshua Reusch wrote:
Am 29.12.2011 19:36, schrieb Andrei Alexandrescu:
On 12/29/11 12:28 PM, Don wrote:
On 28.12.2011 20:00, Andrei Alexandrescu wrote:
Oh, one more thing - one good thing that could come out of this
thread
is abolition (through however slow a deprecation path) of
s.length and
s[i] for narrow strings. Requiring s.rep.length instead of s.length
and
s.rep[i] instead of s[i] would improve the quality of narrow strings
tremendously. Also, s.rep[i] should return ubyte/ushort, not
char/wchar.
Then, people would access the decoding routines on the needed
occasions,
or would consciously use the representation.
Yum.
If I understand this correctly, most others don't. Effectively, .rep
just means, "I know what I'm doing", and there's no change to
existing
semantics, purely a syntax change.
Exactly!
If you change s[i] into s.rep[i], it does the same thing as now.
There's
no loss of functionality -- it's just stops you from accidentally
doing
the wrong thing. Like .ptr for getting the address of an array.
Typically all the ".rep" everywhere would get annoying, so you would
write:
ubyte [] u = s.rep;
and use u from then on.
I don't like the name 'rep'. Maybe 'raw' or 'utf'?
Apart from that, I think this would be perfect.
Yes, I mean "rep" as a short for "representation" but upon first sight
the connection is tenuous. "raw" sounds great.
Now I'm twice sorry this will not happen...
Maybe it could happen if we
1. make dstring the default strings type --
Inefficient.
But correct (enough).
code units and characters would be the same
Wrong.
*sigh*, FINE. Code units and /code points/ would be the same.
Relax.
I'll do one better and ultra relax:
http://www.youtube.com/watch?v=jimQoWXzc0Q
;)
or 2. forward string.length to std.utf.count and opIndex to
std.utf.toUTFindex
Inconsistent and inefficient (it blows up the algorithmic complexity).
Inconsistent? How?
int[]
bool[]
float[]
char[]
I'll refer to another limb of this thread when foobar mentioned a mental
model of strings as strings of letters. Now, given annoying corner
cases, we probably can't get strings of /letters/, but I'd at least like
to make it as far as code points. That seems very doable. I mention
this because I find that forwarding string.length and opIndex would be
much more consistent with this mental model of strings as strings of
unicode code points, which, IMO, is more important than it being binary
consistent with the other things. I'd much rather have char[] behave
more like an array of code points than an array of bytes. I don't need
an array of bytes. That's ubyte[]; I have that already.
char[] is not an array of bytes: it is an array of UTF-8 code units.
Inefficiency is a lot easier to deal with than incorrect. If something
is inefficient, then in the right places I will NOTICE. If something is
incorrect, it can hide for years until that one person (or country, in
this case) with a different usage pattern than the others uncovers it.
so programmers could use the slices/indexing/length (no lazyness
problems), and if they really want codeunits use .raw/.rep (or better
.utf8/16/32 with std.string.representation(std.utf.toUTF8/16/32)
Anyone who intends to write efficient string processing code needs this.
Anyone who does not want to write string processing code will not need
to index into a string -- standard library functions will suffice.
What about people who want to write correct string processing code AND
want to use this handy slicing feature? Because I totally want both of
these. Slicing is super useful for script-like coding.
Except that the proposal would make slicing strings go away.
Yeah, Andrei's proposal says that. But I'm speaking of Joshua's:
so programmers could use the slices/indexing/length ...
I kind-of like either, but I'd prefer Joshua's suggestion.
But generally I liked the idea of just having an alias for strings...
Me too. I think the way we have it now is optimal. The only reason we
are discussing this is because of fear that uneducated users will write
code that does not take into account Unicode characters above code point
0x80. But what is the worst thing that can happen?
1. They don't notice. Then it is not a problem, because they are
obviously only using ASCII characters and it is perfectly reasonable to
assume that code units and characters are the same thing.
How do you know they are only working with ASCII? They might be /now/.
But what if someone else uses the program a couple years later when the
original author is no longer maintaining that chunk of code?
Then they obviously need to fix the code, because the requirements have
changed. Most of it will already work correctly though, because UTF-8
extends ASCII in a natural way.
Or, you know, we could design the language a little differently and make
this become mostly a non-problem. That would be cool.
It is imo already mostly a non-problem, but YMMV:
void main(){
string s = readln();
int nest = 0;
foreach(x;s){ // iterates by code unit
if(x=='(') nest++;
else if(x==')' && --nest<0) goto unbalanced;
}
if(!nest){
writeln("balanced parentheses");
return;
}
unbalanced:
writeln("unbalanced parentheses");
}
That code is UTF aware, even though it does not explicitly deal with
UTF. I'd claim it is like this most of the time.
2. They get screwed up string output, look for the reason, patch up
their code with some functions from std.utf and will never make the same
mistakes again.
Except they don't. Because there are a lot of programmers that will
never put in non-ascii strings to begin with. But that has nothing to
do with whether or not the /users/ or /maintainers/ of that code will
put non-ascii strings in. This could make some messes.
I have *never* seen an user in D.learn complain about it. They might
have been some I missed, but it is certainly not a prevalent problem.
Also, just because an user can type .rep does not mean he understands
Unicode: He is able to make just the same mistakes as before, even more
so, as the array he is getting back has the _wrong element type_.
You know, here in America (Amurica?) we don't know that other countries
exist. I think there is a large population of programmers here that
don't even know how to enter non-latin characters, much less would think
to include such characters in their test cases. These programmers won't
necessarily be found on the internet much, but they will be found in
cubicles all around, doing their 9-to-5 and writing mediocre code that
the rest of us have to put up with. Their code will pass peer review
(their peers are also from America) and continue working just fine until
someone from one of those confusing other places decides to type in the
characters they feel comfortable typing in. No, there will not be
/tests/ for code points greater than 0x80, because there is no one
around to write those. I'd feel a little better if D herds people into
writing correct code to begin with, because they won't otherwise.
There is no way to 'herd people into writing correct code' and UTF-8 is
quite easy to deal with.
Probably not. I played fast and loose with this a lot in my early D
code. Then this same conversation happened like ~3 years ago on this
newsgroup. Then I learned more about unicode and had a bit of a bitter
taste regarding char[] and how it handled indexing. I thought I could
just index char[]s willy nilly. But no, I can't. And the compiler
won't tell me. It just silently does what I don't want.
How often do you actually need to get, for example, the 10th character
of a string? I think it is a very uncommon operation. If the indexing is
just part of an iteration that looks once at each char and handles some
ASCII characters in certain ways, there is no potential correctness
problem. As soon as code talks about non-ascii characters, it has to be
UTF aware anyway.
Maybe unicode is easy, but we sure as hell aren't born with it, and the
language doesn't give beginners ANY red flags about this.
I find myself pretty fortified against this issue due to having known
about it before anything unpleasant happened, but I don't like the idea
of others having to learn the hard way.
Hm, well. The first thing I looked up when I learned D supports Unicode
is how Unicode/UTF work in detail. After that, the semantics of char[]
were very clear to me.
...
There's another issue at play here too: efficiency vs correctness as a
default.
Here's the tradeoff --
Option A:
char[i] returns the i'th byte of the string as a (char) type.
Consequences:
(1) Code is efficient and INcorrect.
Do you have an example of impactful incorrect code resulting from those
semantics?
Nope. Sorry. I learned about it before it had a chance to bite me.
But this is only because I frequent(ed) the newsgroup and had a good
throw on my dice roll.
I might be wrong, but I somewhat have the impression we might be chasing
phantoms here. I have so far never seen a bug in real world code caused
by inadvertent misuse of D string indexing or slicing.
(2) It requires extra effort to write correct code.
(3) Detecting the incorrect code may take years, as these errors can
hide easily.
None of those is a direct consequence of char[i] returning char. They
are the consequence of at least 3 things:
1. char[] is an array of char
2. immutable(char)[] is the default string type
3. the programmer does not know about 1. and/or 2.
I say, 1. is inevitable. You say 3. is inevitable. If we are both right,
then 2. is the culprit.
I can get behind this.
Honestly I'd like the default string type to be intelligent and optimize
itself into whichever UTF-N encoding is optimal for content I throw into
it. Maybe this means it should lazily expand itself to the narrowest
character type that maintains a 1-to-1 ratio between code units and code
points so that indexing/slicing remain O(1), or maybe it's a bag of
disparate encodings, or maybe someone can think of a better strategy.
Just make it /reasonably/ fast and help me with correctness as much as
possible. If I need more performance or more unicode pedantics, I'll do
my homework then and only then.
Of course this is probably never going to happen I'm afraid. Even the
problem of making such a (probably) struct work at compile time in
templates as if it were a native type... agh, headaches.
Option B:
char[i] returns the i'th codepoint of the string as a (dchar) type.
Consequences:
(1) Code is INefficient and correct.
It is awfully optimistic to assume the code will be correct.
(2) It requires extra effort to write efficient code.
(3) Detecting the inefficient code happens in minutes. It is VERY
noticable when your program runs too slowly.
Except when in testing only small inputs are used and only 2 years later
maintainers throw your program at a larger problem instance and wonder
why it does not terminate. Or your program is DOS'd. Polynomial blowup
in runtime can be as large a problem as a correctness bug in practice
just fine.
I see what you mean there. I'm still not entirely happy with it though.
I don't think these are reasonable requirements. It sounds like forced
premature optimization to me.
It is using a better algorithm that performs faster by a linear factor.
I would be very leery of something that looks like a constant time array
indexing operation take linear time. I think premature optimization is
about writing near-optimal hard-to-debug and maintain code that only
gains some constant factors in parts of the code that are not
performance critical.
I have found myself in a number of places in different problem domains
where optimality-is-correctness. Make it too slow and the program isn't
worth writing. I can't imagine doing this for workloads I can't test on
or anticipate though: I'd have to operate like NASA and make things 10x
more expensive than they need to be.
Correctness, on the other hand, can be easily (relatively speaking)
obtained by only allowing the user to input data you can handle and then
making sure the program can handle it as promised. Test, test, test, etc.
This is how I see it.
And I really like my correct code. If it's too slow, and I'll /know/
when it's too slow, then I'll profile->tweak->profile->etc until the
slowness goes away. I'm totally digging option B.
Those kinds of inefficiencies build up and make the whole program run
sluggish, and it will possibly be to late when you notice.
I get the feeling that the typical divide-and-conquer profiling strategy
will find the more expensive operations /at least/ most of the time.
Unfortunately, I have only experience to speak from on this matter.
Yes, what I meant is, that if the inefficiencies are spread out more or
less uniformly, then fixing it all up might seem to be too much work and
too much risk.
Option B is not even on the table. This thread is about a breaking
interface change and special casing T[] for T in {char, wchar}.
Yeah, I know. I'm refering to what Joshua wrote, because I like option
B. Even if it's academic, I'll say I like it anyways, if only for the
sake of argument.
OK.
