Re: fixedstring: a @safe, @nogc string type
now available on dub: https://code.dlang.org/packages/fixedstring
Re: fixedstring: a @safe, @nogc string type
On Wed, Jan 12, 2022 at 07:55:41PM +, Moth via Digitalmars-d-announce wrote: > On Tuesday, 11 January 2022 at 17:55:28 UTC, H. S. Teoh wrote: [...] > > One minor usability issue I found just glancing over the code: many > > of your methods take char[] as argument. Generally, you want > > const(char)[] instead, so that it will work with both char[] and > > immutable(char)[]. No reason why you can't copy some immutable chars > > into a FixedString, for example. > > they should all already be `in char[]`? i've added a test to confirm > it works with both `char[]` and `immutable(char)[]` and it compiles > fine. [...] Oh you're right! I totally missed that. Sorry, my bad. T -- Talk is cheap. Whining is actually free. -- Lars Wirzenius
Re: fixedstring: a @safe, @nogc string type
On Wednesday, 12 January 2022 at 19:55:41 UTC, Moth wrote: [snip] Another issue is the way concatenation is implemented. Since FixedStrings have compile-time size, this potentially means every time you concatenate a string in your code you get another instantiation of FixedString. This can lead to a LOT of template bloat if you're not careful, which may quickly outweigh any benefits you may have gained from not using the built-in strings. oh dear, that doesn't sound good. i hadn't considered that at all. i'm not sure how to even begin going about fixing that... One thing you could potentially do is to round the size of the result up to, say, a power of two. That way, instead of instantiating a new template for every individual string length, you only instantiate `FixedString!16`, `FixedString!32`, `FixedString!64`, etc. Of course, doing this will leave you with some wasted memory at runtime. So you will probably want to run some benchmarks to compare performance before and after.
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 17:55:28 UTC, H. S. Teoh wrote: [snip] One minor usability issue I found just glancing over the code: many of your methods take char[] as argument. Generally, you want const(char)[] instead, so that it will work with both char[] and immutable(char)[]. No reason why you can't copy some immutable chars into a FixedString, for example. they should all already be `in char[]`? i've added a test to confirm it works with both `char[]` and `immutable(char)[]` and it compiles fine. [snip] Another issue is the way concatenation is implemented. Since FixedStrings have compile-time size, this potentially means every time you concatenate a string in your code you get another instantiation of FixedString. This can lead to a LOT of template bloat if you're not careful, which may quickly outweigh any benefits you may have gained from not using the built-in strings. oh dear, that doesn't sound good. i hadn't considered that at all. i'm not sure how to even begin going about fixing that...
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 12:22:36 UTC, WebFreak001 wrote: [snip] you can relatively easily find out how many bytes a string takes up with `std.utf`. You can also iterate by code points or graphemes there if you want to translate some kind of character index to byte position. HOWEVER it's not clear what a character is. Sure for the posted cases here it's no problem but when it comes to languages based on combining glyphs together to form new glyphs it's no longer clear what is a character. There are Graphemes (grapheme clusters) which are probably the closest to what everybody would think a character is, but IIRC there are edge cases with that a programmer wouldn't expect, like adding a character not increasing the count of characters of the string because it merges with the last Grapheme. Additionally there is a performance impact on using Graphemes over simpler things like codepoints which fit 98% of use-cases with strings. Codepoints in D are mapped 1:1 using dchar, take up to 2 wchars or up to 4 chars. You can use `std.utf` to compute byte lengths for a codepoint given a string. aha, i think i might have miscommunicated here - i was talking about an error i thought i was having where a fixedstring of `"áéíóú"` wasn't equal to a string literal of the same, but as it turned out i was misreading the error message [i had been trying to assign a literal larger than the fixedstring could take]. to tell the truth, unicode awareness is... not something i really want to mess with right now, lol. it would be nice to have the option at some point in the future though. I would rather suggest you support FixedString with types other than `char`. (wchar, dchar, heck users could even use any arbitrary type and use this as array class) For languages that commonly use more than 1 byte per codepoint or for interop with Win32 unicode APIs, JavaScript strings, C# strings, UTF16 files in general, etc. programmers might opt to use FixedString with wchar then. With D's templates that should be quite easy to do (add a template parameter to the struct like `struct FixedString(size_t maxSize, CharT = char)` and replace all usage of char in your code with `CharT` in this case) [i've pushed an update to the repo for this!](https://github.com/Moth-Tolias/fixedstring/releases/tag/v1.1.0) =] it was a bit more complicated than a simple replace all, but not too hard.
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 17:55:28 UTC, H. S. Teoh wrote:
Generally, I'd advise not conflating your containers with
ranges over your containers: I'd make .opSlice return a
traditional D slice (i.e., const(char)[]) instead of a
FixedString, and just require writing `[]` when you need to
iterate over the string as a range:
FixedString!64 mystr;
foreach (ch; mystr[]) { // <-- iterates over const(char)[]
...
}
This way, no redundant copying of data is done during iteration.
It already does this. In D2, `[]` is handled by a zero-argument
`opIndex` overload, not by `opSlice`. [1] FixedString has such an
overload [2], and it does, in fact, return a slice.
[1] https://dlang.org/spec/operatoroverloading.html#slice
[2]
https://github.com/Moth-Tolias/fixedstring/blob/v1.0.0/source/fixedstring.d#L105
Re: fixedstring: a @safe, @nogc string type
On Tue, Jan 11, 2022 at 11:16:13AM +, Moth via Digitalmars-d-announce wrote:
> On Tuesday, 11 January 2022 at 03:20:22 UTC, Salih Dincer wrote:
> > [snip]
>
> glad to hear you're finding it useful! =]
One minor usability issue I found just glancing over the code: many of
your methods take char[] as argument. Generally, you want const(char)[]
instead, so that it will work with both char[] and immutable(char)[].
No reason why you can't copy some immutable chars into a FixedString,
for example.
Another potential issue is with the range interface. Your .popFront is
implemented by copying the entire buffer 1 char forwards, which can
easily become a hidden performance bottleneck. Iteration over a
FixedString currently is O(N^2), which is a problem if performance is
your concern.
Generally, I'd advise not conflating your containers with ranges over
your containers: I'd make .opSlice return a traditional D slice (i.e.,
const(char)[]) instead of a FixedString, and just require writing `[]`
when you need to iterate over the string as a range:
FixedString!64 mystr;
foreach (ch; mystr[]) { // <-- iterates over const(char)[]
...
}
This way, no redundant copying of data is done during iteration.
Another issue is the way concatenation is implemented. Since
FixedStrings have compile-time size, this potentially means every time
you concatenate a string in your code you get another instantiation of
FixedString. This can lead to a LOT of template bloat if you're not
careful, which may quickly outweigh any benefits you may have gained
from not using the built-in strings.
> hm, i'm not sure how i would go about fixing that double character
> issue. i know there's currently some wierdness with wchars / dchars
> equality that needs to be fixed [shouldn't be too much trouble, just
> need to set aside the time for it], but i think being able to tell how
> many chars there are in a glyph requires unicode awareness? i'll look
> into it.
[...]
Yes, you will require Unicode-awareness, and no, it will NOT be as
simple as you imagine.
First of all, you have the wide-character issue: if you're dealing with
anything outside of the ASCII range, you will need to deal with code
points (potentially wchar, dchar). You can either take the lazy way out
(FixedString!(n, wchar), FixedString!(n, dchar)), but that will
exacerbate your template bloat very quickly. Plus, it wastes a lot of
memory, esp. if you start using dchar[] -- 4 bytes per character
potentially makes ASCII strings use up 4x more memory. (And even if you
decide using dchar[] isn't a concern, there's still the issue of
graphemes -- see below, which requires non-trivial decoding anyway.)
Or you can handle UTF-8, which is a better solution in terms of memory
usage. But then you will immediately run into the encoding/decoding
problem. Your .opSlice, for example, will not work correctly unless you
auto-decode. But that will be a performance hit -- this is one of the
design mistakes in hindsight that's still plaguing Phobos today. IMO the
better approach is to iterate over the string *without* decoding, but
just detecting codepoint boundaries. Regardless, you will need *some*
way of iterating over code points instead of code units in order to deal
with this properly.
But that's only the beginning of the story. In Unicode, a "code point"
is NOT what most people imagine a "character" is. For most European
languages this is the case, but once you go outside of that, you'll
start finding things like accented characters that are composed of
multiple code points. In Unicode, that's called a Grapheme, and here's
the bad news: the length of a Grapheme is technically unbounded (even
though in practice it's usually 2 or occasionally 3 -- but you *will*
find more on rare occasions). And worst of all, determining the length
of a grapheme requires an expensive, non-trivial algorithm that will
KILL your performance if you blindly do it every time you traverse your
string.
And generally, you don't *want* to do grapheme segmentation anyway --
most code doesn't even care what the graphemes are, it just wants to
treat strings as opaque data that you may occasionally want to segment
into substrings (and substrings don't necessarily require grapheme
segmentation to compute, depending on what the final goal is). But
occasionally you *will* need grapheme segmentation (e.g., if you need to
know how many visual "characters" there are in a string); for that, you
will need std.uni. And no, it's not something you can implement
overnight. It requires some heavy-duty lookup tables and a (very
careful!) implementation of TR14.
Because of the foregoing, you have at least 4 different definitions of
the length of the string:
1. The number of code units it occupies, i.e., the number of chars /
wchars / dchars.
2. The number of code points it contains, which, in UTF-8, is a
non-trivial quantity that requires iterating over the entire string to
compute. Or
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 11:16:13 UTC, Moth wrote: On Tuesday, 11 January 2022 at 03:20:22 UTC, Salih Dincer wrote: [snip] glad to hear you're finding it useful! =] hm, i'm not sure how i would go about fixing that double character issue. i know there's currently some wierdness with wchars / dchars equality that needs to be fixed [shouldn't be too much trouble, just need to set aside the time for it], but i think being able to tell how many chars there are in a glyph requires unicode awareness? i'll look into it. [...] you can relatively easily find out how many bytes a string takes up with `std.utf`. You can also iterate by code points or graphemes there if you want to translate some kind of character index to byte position. HOWEVER it's not clear what a character is. Sure for the posted cases here it's no problem but when it comes to languages based on combining glyphs together to form new glyphs it's no longer clear what is a character. There are Graphemes (grapheme clusters) which are probably the closest to what everybody would think a character is, but IIRC there are edge cases with that a programmer wouldn't expect, like adding a character not increasing the count of characters of the string because it merges with the last Grapheme. Additionally there is a performance impact on using Graphemes over simpler things like codepoints which fit 98% of use-cases with strings. Codepoints in D are mapped 1:1 using dchar, take up to 2 wchars or up to 4 chars. You can use `std.utf` to compute byte lengths for a codepoint given a string. I would rather suggest you support FixedString with types other than `char`. (wchar, dchar, heck users could even use any arbitrary type and use this as array class) For languages that commonly use more than 1 byte per codepoint or for interop with Win32 unicode APIs, JavaScript strings, C# strings, UTF16 files in general, etc. programmers might opt to use FixedString with wchar then. With D's templates that should be quite easy to do (add a template parameter to the struct like `struct FixedString(size_t maxSize, CharT = char)` and replace all usage of char in your code with `CharT` in this case)
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 11:16:13 UTC, Moth wrote: On Tuesday, 11 January 2022 at 03:20:22 UTC, Salih Dincer wrote: [snip] glad to hear you're finding it useful! =] ... i know there's currently some wierdness with wchars / dchars equality that needs to be fixed [shouldn't be too much trouble... If you try mixing char/wchar/dchar, you need encoding/decoding for utf-8, utf-16 and utf-32 ( maybe even LE/BE ). It become complicated very fast...
Re: fixedstring: a @safe, @nogc string type
On Tuesday, 11 January 2022 at 03:20:22 UTC, Salih Dincer wrote: [snip] glad to hear you're finding it useful! =] hm, i'm not sure how i would go about fixing that double character issue. i know there's currently some wierdness with wchars / dchars equality that needs to be fixed [shouldn't be too much trouble, just need to set aside the time for it], but i think being able to tell how many chars there are in a glyph requires unicode awareness? i'll look into it. what's your usecase for usefulCapacity()?
Re: fixedstring: a @safe, @nogc string type
On Monday, 10 January 2022 at 12:55:28 UTC, Moth wrote:
have fun =]
https://github.com/Moth-Tolias/fixedstring
I try Fixedstring and, to my great relief I got the results I
expected. Thank you, good luck with your work.
So how to fix this double character issue:
```d
FixedString!6 sugar = "şeker"; // in Turkish
assert(sugar[0..3] == "şe");
FixedString!5 şeker = "sugar"; // in English
assert(şeker[0..2] == "su");
assert(sugar.length > şeker.length);
```
How about adding that member among FixedString?
```d
public size_t usefulCapacity()const pure @nogc @safe
{
return size - _length;
}
```
Re: fixedstring: a @safe, @nogc string type
On Monday, 10 January 2022 at 14:06:27 UTC, Moth wrote:
On Monday, 10 January 2022 at 13:12:13 UTC, jmh530 wrote:
You might add some examples to the Readme.md
good observation, i'll work on that. in the meantime the
examples in the unittests should suffice.
fixed.
for those who don't want to visit the github just to see the
change, here's the example code:
```d
void main() @safe @nogc nothrow
{
FixedString!14 foo = "clang";
foo[0] = 'd';
foo ~= " is cool";
assert (foo == "dlang is cool");
foo.length = 9;
auto bar = FixedString!4("neat");
assert (foo ~ bar == "dlang is neat");
}
```
Re: fixedstring: a @safe, @nogc string type
On Monday, 10 January 2022 at 13:12:13 UTC, jmh530 wrote: You might add some examples to the Readme.md good observation, i'll work on that. in the meantime the examples in the unittests should suffice.
Re: fixedstring: a @safe, @nogc string type
On Monday, 10 January 2022 at 12:55:28 UTC, Moth wrote: hi all. i got fed up with the built-in string type having so many features unavailable in `@nogc` code, so i made my own. introducing fixedstring: a templated fixed-length array of `char`s, compatible with `@safe`, `@nogc`, and `nothrow` code. licenced under the AGPL-3.0 or later, but i'm open to relicensing if someone really really wants it. have fun =] https://github.com/Moth-Tolias/fixedstring [snip] You might add some examples to the Readme.md
Re: fixedstring: a @safe, @nogc string type
On Monday, 10 January 2022 at 12:55:28 UTC, Moth wrote: hi all. Good.Let's use `betterC`.
