Re: std.file.read returns void[] why?
On Thursday, 17 April 2014 at 21:27:44 UTC, Steven Schveighoffer wrote: On Thu, 17 Apr 2014 17:04:25 -0400, monarch_dodra monarchdo...@gmail.com wrote: void[] will only make sense once you've accepted that void.sizeof == 1. It is already accepted that when we talk about length in a void[], it's the number of bytes. But the data has no formal type. Well, I always thought that void[] slice meant there are slice.length items, starting at slice.ptr. I don't know the size of the individual items. For example, in C, a lot of functions take void* first, size_t num, size_t width. In fact, most of druntime functions take void[] buffers that work that way. There's an associated typeid, so that you can now how large each individual items are. But any array implicitly casts to void[]. This is why it makes a good parameter for read or write (when reading or writing the binary data). I guess. I just find it kind of strange that a type that has no type would have an actual sizeof. Then again, I thought void had no sizeof in C, but I just checked, and I was wrong. Well, I guess void[] is C++'s char* for indiscriminate buffers. Speaking of which, does void* trigger strict aliasing in D? This subject seems like a hot potato no-one wants to touch. No, it's equivalent to void *, not char *. in D, ubyte[] would be the equivalent of C's char *. -Steve Correct.
Re: std.file.read returns void[] why?
On Fri, 18 Apr 2014 02:04:16 -0400, monarch_dodra monarchdo...@gmail.com
wrote:
On Thursday, 17 April 2014 at 21:27:44 UTC, Steven Schveighoffer wrote:
On Thu, 17 Apr 2014 17:04:25 -0400, monarch_dodra
monarchdo...@gmail.com wrote:
void[] will only make sense once you've accepted that void.sizeof ==
1.
It is already accepted that when we talk about length in a void[], it's
the number of bytes. But the data has no formal type.
Well, I always thought that void[] slice meant there are slice.length
items, starting at slice.ptr. I don't know the size of the individual
items.
For example, in C, a lot of functions take void* first, size_t num,
size_t width.
In fact, most of druntime functions take void[] buffers that work that
way. There's an associated typeid, so that you can now how large each
individual items are.
import std.stdio;
void main()
{
int[] x = new int[5];
void[] y = x;
writeln(y.length); // 20
}
When a function takes a typeid, that usually is because the translation is
not made. In druntine cases, the compiler is removing the type, and
sticking it into the typeid instead. But the length has not been
translated to bytes! It's still in terms of the original type.
In those cases, it's equivalent to:
void[] y = *cast(void[]*)x;
which would make y.length == 5.
But any array implicitly casts to void[]. This is why it makes a good
parameter for read or write (when reading or writing the binary data).
I guess. I just find it kind of strange that a type that has no type
would have an actual sizeof. Then again, I thought void had no sizeof in
C, but I just checked, and I was wrong.
It's a little strange, but while void has no size, void[] *does* have a
size. The size is in bytes. You can think of an array as starts at this
address, and ends at that address. Because addresses are in terms of
bytes, so is the length of that array.
I admit, I didn't think C's void had a size ;) I'm pretty sure it doesn't
in D, but then again...
-Steve
Re: Dynamically Sized Structs
On Fri, 18 Apr 2014 00:05:03 -0400, Kagamin s...@here.lot wrote: Well, it's proof of concept of bound checked variable-size struct, I wrote it in a minute. It even compiles and runs. Please take no offense :) I just was pointing out a difference between a hand-managed and hand-written struct that I might have written and the one that you created. Depending on usage, yours might be sufficient. Note, you could probably, with mixin magic, make a version that could be emplaced inside a struct or class without an extra indirection. -Steve
Re: std.file.read returns void[] why?
On Friday, 18 April 2014 at 13:08:04 UTC, Steven Schveighoffer wrote: I admit, I didn't think C's void had a size ;) I'm pretty sure it doesn't in D, but then again... -Steve Yeah... static assert(void.sizeof == 1); passes :/ So in any case, long story short: void[]: This is an un-typed buffer, pointing to a memory location that starts at .ptr, and is .length bytes in length. Also, as far as the GC is concerned, void is a type that should be scanned (whether or not the data originally allocated was marked as such is another issue).
Re: Dynamically Sized Structs
Oh, and I don't believe, that a variable-size struct can be emplaced inside fixed-size struct or class. Only as a smart pointer from the example.
Re: Dynamically Sized Structs
I mean, it doesn't cover all scenarios, but can be extended to support them. The indexes array does just that: it's emplaced without indirection, but still is bound checked.
Re: Dynamically Sized Structs
On Friday, 18 April 2014 at 13:10:28 UTC, Steven Schveighoffer wrote: Note, you could probably, with mixin magic, make a version that could be emplaced inside a struct or class without an extra indirection. Speaking about mixin magic, you probably suggest to do it overly generically, though it seems, use cases for variable size structs are specialized, specialized code and specialized data structures, so I suspect specialized approach will be more productive, intuitive, understandable, simple and straightforward for such tasks, generic approach is probably inadequate here. But if you can do it, you can try.
On Concurrency
Could someone please give some references to thorough explainings on these latest concurrency mechanisms - Go: Goroutines - Coroutines (Boost): - https://en.wikipedia.org/wiki/Coroutine - http://www.boost.org/doc/libs/1_55_0/libs/coroutine/doc/html/coroutine/intro.html - D: core.thread.Fiber: http://dlang.org/library/core/thread/Fiber.html - D: vibe.d and how they relate to the following questions: 1. Is D's Fiber the same as a coroutine? If not, how do they differ? 2. Typical usecases when Fibers are superior to threads/coroutines? 3. What mechanism does/should D's builtin Threadpool ideally use to package and manage computations? 4. I've read that vibe.d's has a more lightweight mechanism than what core.thread.Fiber provides. Could someone explain to me the difference? When will this be introduced and will this be a breaking change? 5. And finally how does data sharing/immutability relate to the above questions?
Re: Dynamically Sized Structs
On Fri, 18 Apr 2014 12:59:35 -0400, Kagamin s...@here.lot wrote: Oh, and I don't believe, that a variable-size struct can be emplaced inside fixed-size struct or class. Only as a smart pointer from the example. It goes at the end. Then you need to allocate the whole thing with that in mind. -Steve
Re: On Concurrency
Correction: The references I gave _are_ theoretically thorough, so I'm satisified with these for now. I'm however still interested in the D-specific questions I asked.
Reducing an array
Hi there, I try to remove all equal elements of an array, thus [2,2] -- [2]. I thought this maybe would be possible with std.algorithm.reduce, but at least the way I tried it doesn't work: arr.reduce( (a,b) = a != b ); Is there a simple solution using Phobos-functions? Thank you, Tim
Re: Reducing an array
On Thu, 17 Apr 2014 09:46:25 -0400, Tim Holzschuh via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: Hi there, I try to remove all equal elements of an array, thus [2,2] -- [2]. I thought this maybe would be possible with std.algorithm.reduce, but at least the way I tried it doesn't work: arr.reduce( (a,b) = a != b ); reduce doesn't do what you think it does. It applies a function to all elements, keeping track of the result of each function call, and passing it to the next one. In other words, reduce!fn(a, range) is like doing this: fn(range[5], fn(range[4], fn(range[3], fn(range[2], fn(range[1], fn(range[0], a)); What you want is probably uniq: http://dlang.org/library/std/algorithm/uniq.html Note that it works on a SORTED range, so you want to sort first. Note also that what it returns is not an array, but a lazily iterated range over the array. If you want another array, this is the code I would use: arr.sort(); arr = arr.uniq.array(); -Steve
Re: Reducing an array
On Friday, 18 April 2014 at 20:27:20 UTC, Steven Schveighoffer wrote: Note also that what it returns is not an array, but a lazily iterated range over the array. If you want another array, this is the code I would use: arr.sort(); arr = arr.uniq.array(); -Steve Out of curiosity, if the requirement was to *also* preserve ordering (eg: remove all non-first elements), how would you go at it? [2, 1, 1, 3, 2, 3] = [2, 1, 3]; Maybe std.algorithm's `makeIndex` would help here? Bonus points for doing it inplace.
Re: Reducing an array
monarch_dodra:
Out of curiosity, if the requirement was to *also* preserve
ordering (eg: remove all non-first elements), how would you go
at it?
[2, 1, 1, 3, 2, 3] = [2, 1, 3];
Maybe std.algorithm's `makeIndex` would help here?
Bonus points for doing it inplace.
This preserves ordering and it's in-place. Not tested much:
void main() {
import std.stdio, std.traits;
auto data = [2, 1, 1, 3, 2, 3];
bool[ForeachType!(typeof(data))] seen;
size_t pos = 0;
foreach (immutable i; 0 .. data.length)
if (data[i] !in seen) {
if (pos != i)
data[pos] = data[i];
seen[data[i]] = true;
pos++;
}
data.length = pos;
data.writeln;
}
Bye,
bearophile
arrays in DMD V2
import std.stdio;
void main()
{
inta0[];
inta1[][];
string a2[][];
string a3[][string];
string a4[][string][string];
//string a4[string][string][string]; is this the same as above
inta5[][string][string][string];
inta6[string][int][string][float];
inta7[int][int][string];
// how do you initialize each array, what type are they
multidimensional???
// how do you define all of the above with limits on each
dimension???
}
//help please
Re: arrays in DMD V2
On Saturday, 19 April 2014 at 00:27:32 UTC, steven kladitis wrote:
import std.stdio;
void main()
{
inta0[];
inta1[][];
string a2[][];
string a3[][string];
string a4[][string][string];
//string a4[string][string][string]; is this the same as
above
inta5[][string][string][string];
inta6[string][int][string][float];
inta7[int][int][string];
// how do you initialize each array, what type are they
multidimensional???
// how do you define all of the above with limits on each
dimension???
}
//help please
First, don't use that syntax. everything should be placed on the
type:
Second,
void main() {
inta5[][string][string][string];
pragma(msg, typeof(a5));
}
Third,
http://dlang.org/arrays.html
http://dlang.org/hash-map.html
Re: arrays in DMD V2
Thanks, I am trying to understand what I am doing. The docs seem
unclear to me on how to initialize these. I think there are
three ways.
with brackets , the other with foreach or direct assignments.
-- here is a longer version
-- uncomment out the assignments to see the errors I get.
-- I am trying to understand arrays.
On Saturday, 19 April 2014 at 01:13:55 UTC, Jesse Phillips wrote:
On Saturday, 19 April 2014 at 00:27:32 UTC, steven kladitis
wrote:
import std.stdio;
void main()
{
inta0[];
inta1[][];
string a2[][];
string a3[][string];
string a4[][string][string];
//string a4[string][string][string]; is this the same as
above
inta5[][string][string][string];
inta6[string][int][string][float];
inta7[int][int][string];
// how do you initialize each array, what type are they
multidimensional???
// how do you define all of the above with limits on each
dimension???
}
//help please
First, don't use that syntax. everything should be placed on
the type:
Second,
void main() {
inta5[][string][string][string];
pragma(msg, typeof(a5));
}
Third,
http://dlang.org/arrays.html
http://dlang.org/hash-map.html
Re: arrays in DMD V2
import std.stdio;
void main()
{
inta0[];
inta1[][];
string a2[][];
string a3[][string];
string a4[][string][string];
//string a4[string][string][string]; is this the same as above
inta5[][string][string][string];
inta6[string][int][string][float];
inta7[int][int][string];
// how do you initialize each array, what type are they
multidimensional???
// how do you define all of the above with limits on each
dimension???
a0 = [1,2,3];
//writefln( a0 );
a1 = [ [ 1,2,3 ],[4,5,6]];
//writefln( a1 );
a2 = [ [a,b ],[ c,d ] ];
//writefln ( a2 );
//a3 = [ [a,b ],[ c,d ] ];
// does not work
//a4= [ [a,b ];
// does not work.
//a5 = [ [1,a,b]];
pragma(msg, typeof(a0));
pragma(msg, typeof(a1));
pragma(msg, typeof(a2));
pragma(msg, typeof(a3));
pragma(msg, typeof(a4));
pragma(msg, typeof(a5));
pragma(msg, typeof(a6));
pragma(msg, typeof(a7));
// does not work
//a6= [ 1,[a,1,b,4.0]];
// does not work
//a7 = [ 1,1,a];
// does not work
// also how would you do in a foreach?
}
