Marc Schütz:
auto sums = input
.transposed
.map!(a => a.sum);
And that part is better written:
.map!sum;
I also suggest to align the leading dot to the precedent line:
auto sums = input
.transposed
.map!
Marc Schütz:
int[][] input = new int[][2];
input[0] = [1, 2, 3, 4];
input[1] = [5, 6, 7, 8];
writeln(input);
auto sums = input
.transposed
.map!(a => a.sum);
writeln(sums);
}
Output:
[[1, 2, 3, 4], [5, 6,
Marc Schütz:
We'd need something taking and returning a RoR that "mirrors"
them diagonally. Then we could simply apply `map!(r => r.sum)`
on the result.
A simple solution is to create a row of values, and then sum them
correctly while you scan the rows.
Bye,
bearophile
Misu:
void main(string[] args)
{
class Account
{
public this(int id) { this.id = id; }
int id;
}
...
This is not an answer to your question, but note:
void main() {
class Foo {}
static class Bar {}
pragma(msg, __traits(classI
Justin Whear:
--any compiler crash is a bug
regardless of whether the source is valid D code or not.
I suspect that in some cases those compiler crashes are a way for
the compiler to tell the programmer that the code was too much
hairy and too much hard to understand ;-)
Bye,
bearophile
Bauss:
Is there any way to track down access violations, instead of me
having to look through my source code manually.
I have a pretty big source code and an access violation happens
at runtime, but it's going to be a nightmare looking through it
all to find the access violation. Not to ment
Ali Çehreli:
Perhaps I am expecting too much from the current 'in' contract
design and implementation. ;)
The "in contract" is named pre-condition, or precondition.
Bye,
bearophile
Jonathan M Davis:
That loses the ability to test which type of range you're
talking about.
Yes, one can think about templates like "isForwardRangeOf", etc.
But for such specialized cases I think using
isForwardRange+is(ElementType) is acceptable and avoids adding
too many templates to Phobo
Sometimes I have a function that needs an iterable:
void foo(Range)(Range data)
if (isForwardRange!Range && is(Unqual!(ForeachType!Range) ==
int)) {}
So is it a good idea to add a "isRangeOf" template to Phobos?
void foo(Range)(Range data)
if (isRangeOf!(Range, int)) {}
Bye,
bearophile
Xinok:
My concern is that SortedRange only accepts a range which is
random-access and limits its functionality to those primitives.
Concatenation is not required for random-access ranges, so
should we expect SortedRange to overload this operator?
I understand, that's why I am asking this her
Ola Fosheim Grøstad:
Shouldn't sorted range maintain the invariant automatically in
order to remain typesafe?
Yes, of course.
Bye,
bearophile
I have often arrays that are sorted, and sometimes I'd like to
append items to them. So I'd like to write something like:
SortedRange!(Foo[], q{ a.x < b.x }) data;
data ~= Foo(5);
immutable n = data.upperBound(Foo(2)).length;
This means having an array of Foos as sorted range, and appending
Steven Schveighoffer:
long a = src.countUntil(start);
if (a < 0)
return src; // null
a += start.length;
long b = src[a..$].countUntil(end);
I think there it's better to use "auto" instead of "long".
Bye,
bearophile
advibm:
I would like to have something like that:
char[] buf; // already filled array
char[] partOfBuf = betweenTwoStrings(buf, "START", "END");
partOfBuf[0] = 'a'; // THIS should also change the 'buf'
variable
assert(buf[0] == 'a');
Thanks for your help
To do this you don't need to return
Shriramana Sharma:
int i ;
ref ir = i ;
// Error: variable ref_type.main.ir only parameters or foreach
declarations can be ref
// Comment: add ", return values" after "parameters"
}
I like this.
Bye,
bearophile
Etienne Cimon:
So what's the point of making a class or methods final?
It forbids subclassing. And final methods are not virtual, so
they can be inlined.
Bye,
bearophile
Etienne Cimon:
I'm not sure, why does a final class carry a vtable pointer?
In D all class instances contain a pointer to the class and a
monitor pointer. The table is used for run-time reflection, and
for standard virtual methods like toString, etc.
Bye,
bearophile
Jonathan M Davis:
Questions like this have come up and been discussed before, but
using the same parameter names as member variable names for
constructors is such a common practice that there would be
quite a bit of screaming if we didn't allow it.
I'm willing to hear them scream. D should s
Neal:
Interesting! Thank you. Memory isn't a problem
Unfortunately currently the sort-decorate-undercorate in Phobos
is not very fast.
but I would still
like to learn how to write more efficient programs. If i posted
my code would you be able to give me some advice?
There is far more th
neal:
data.sort!q{ to!int(a[4]) > to!int(b[4]) };
This code fixes my problem! Thanks for the quick responses
guys. you rock!
That converts string->int many more than once for each string. So
if memory is not a problem, consider using a
decorate-sort-undecorate pattern:
data.schwartzSort!
neal:
Anybody have any suggestions?
Something like this, perhaps?
data.sort!q{ a[4] > b[4] };
Bye,
bearophile
Szymon Gatner:
const int[] a;
int[] b;
static this()
{
b = [1];
a = b;
}
Ant this code works? What is the point of const then if you can
assign it to mutable slice?
It works, and I think it should work. Inside the (module)
constructor the const state is handled differently.
Thank
Minas Mina:
Aren't pure functions supposed to return the same result every
time? If yes, it is correct to not accept it.
But how can main() not be pure? Or, how can't the 'a' array be
immutable?
Bye,
bearophile
Currently this code gets rejected:
const int[] a = [1];
void main() pure {
auto y = a[0];
}
test2.d(3,14): Error: pure function 'D main' cannot access
mutable static data 'a'
test2.d(3,14): Error: pure function 'D main' cannot access
mutable static data 'a'
But is this a good idea? Isn'
Nordlöw:
It would be nice to have a lambda-variant of std.string.tr to
call like
x.tr!isWhite(['_'])
If your text is ASCII, then there is std.ascii.whitespace that
can be given as argument to std.string.tr.
Bye,
bearophile
Justin Whear:
std.string.squeeze might be more appropriate.
But with tr you can also replace the spaces with the underscore.
Bye,
bearophile
Nordlöw:
How can I extend
string line = "carwash";
line.strip.splitter!isWhite.joiner("_").to!string
so that
car wash
becomes
car_wash
and not
car___wash
?
Use std.string.tr.
Bye,
bearophile
John Carter:
Your paste has expired / no longer there but the subject
has come up again...
...
Do you still have your implementation hanging around?
I think it was this. *Untested*:
void main(string[] args) {
import core.stdc.stdio, std.bigint, core.stdc.stdlib;
immutable n = (
Ola Fosheim Grøstad:
The IDE support is probably a bit better with Java/C#
The importance of the IDE for the first language is
controversial. I think it's not so important.
and using a statically typed language as your first language
has advantages,
While no one has determined scientifi
RBfromME:
I'm a newbie to programming and have been looking into the D
lang as a general purposing language to learn, yet the D
overview indicates that java would be a better language to
learn for your first programming language. Why? Looks like D
is easier than Java...
Python is probably
Domingo:
Ideally I want to use something like this:
-
import std.stdio;
import std.string;
import std.algorithm;
import std.conv;
void main()
{
string[] ar = [" dad ", " blue "];
writeln(typeid(ar));
//ar.each(writeln);
//ar.map!writeln;
ketmar:
is there any hack/trick to determine if variable is __gshared?
or if it is a thread-local, for that matter?
There is the -vtls compiler switch.
Bye,
bearophile
Ali Çehreli:
foreach (i, element; MyRange(42).enumerate) {
// ...
}
versus sequence!"n" and zip:
foreach (i, element; zip(sequence!"n", MyRange(42))) {
// ...
}
But it's better to not use automatic unpacking of tuples. See
issues 7361 and especially 9817.
B
yawniek:
i found two snippets from the functional docs that do not work
(anymore?)
http://dlang.org/phobos/std_functional.html
assert(compose!(map!(to!(int)), split)("1 2 3") == [1, 2, 3]);
and
int[] a = pipe!(readText, split, map!(to!(int)))("file.txt");
throwing a std.array.array into the
ketmar:
additionally to all bearophile said, there is another
interesting thing in D: special string literals for hex data.
immutable ubyte[] n = cast(typeof(n))x"deadf00d";
or even:
immutable ubyte[] n = cast(typeof(n))x"de ad f 0 0 d";
spaces doesn't matter, only digits do.
The prob
Marc Schütz:
It's equivalent to:
int[] tmp = a1[] * 3;
int[] a4 = tmp.dup;
The first part is of course identical to line 3, so this should
be an error, too. Normal rules for evaluation order require
`a1[] * 3` to be evaluated before `(...).dup`, so where is it
supposed to store the
You want ubytes (unsigned bytes) because 0x04 is 164 that is
bigger than byte.max.
I'd like bytes to be named sbyte and ubyte in D, but Walter has
refused this.
Bye,
bearophile
Anibal:
byte[] arr = [ 0x00, 0xA4, 0x04];
This throws a int[] to byte[] cast error
You want ubytes (unsigned bytes) because 0x04 is 164 that is
bigger than byte.max.
So use:
ubyte[] arr = [ 0x00, 0xA4, 0x04];
I also tried
byte[] arr = [cast(byte) 0x00, cast(byte)0xA4, cast(byte) 0x04];
Observe:
void main() {
int[3] a1 = [1, 3, 6];
int[] a2 = a1[] * 3; // line 3, Error
int[] a3 = a1.dup[] *= 3; // line 4, OK?
int[] a4 = (a1[] * 3).dup; // line 5, Error
}
Currently the operation in line 4 is accepted:
test.d(3,17): Error: array operation a1[] * 3
anonymous:
You can turn the tuples into ranges with `only`:
writef("%(%(%s %)\n%)", zip(indexes, source).map!(t =>
only(t.expand)));
This is a nice idea. Expand can probably be replaced by a []. I
presume this works only if the types inside the tuple are the
same.
Bye,
bearophile
antropod:
Looks fairly straightforward. But, the second function causes
compilation error:
std.format.FormatException@C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(2
585): Expected '%s' format specifier for type 'Tuple!(uint,
uint)'
Can you help me with that?
Currently the "%(%s%)"
AsmMan:
import myModule : func, func2;
I use this in D to know what I have imported and where is was
imported from.
Bye,
bearophile
Ali Çehreli:
Never mind then.
Well, now the D code is present, so why don't you benchmark it
(but I don't know how much correct it is)? :-)
Bye,
bearophile
Ali Çehreli:
Found on Reddit:
Where's the Reddit thread?
Are you motivated enough to compare D's associative arrays with
those results? :)
D associative arrays are often even slower than CPython ones, so
I don't expect D to shine in this comparison.
This is a D port of the Java code, b
Marc Schütz:
Alternatively, you could create a union with a private and a
public member with the same types, but I wouldn't recommend it.
Besides, the members would need to have different names:
class Foo {
union {
private int a;
public int b;
}
Nordlöw:
should be
Enumerator start = Enumerator.min
This also requires the enum to have adjacent values (in general
enums can skip values).
Bye,
bearophile
Nordlöw:
Have anybody thought about adding safe enum-based indexing to
builtin arrays? Ada has this.
I'd like this. I'd like even more: a general way to have
optionally strongly typed array indexes.
enum I { a=3,b=4,c=5 }
int[I] x = [3,4,5];
In D currently that "int[I]" is an as
Take a look in bugzilla, if it's not already present file it.
https://issues.dlang.org/show_bug.cgi?id=13505
Bye,
bearophile
badlink:
Does this mean that void arrays are a thing or it is a bug ?
You can compile that with:
class Foo {
void[10] x = void;
}
But this code shows a dmd bug (lack of line number):
class Foo {
void[10] x;
}
void main() {}
Error: void does not have a default initializer
Take a
anonymous:
Here, the pointer to the stack escapes the function. Don't do
that!
Hopefully the D type system will be improved with scoping
tracking & management, to turn similar operations into
compilation errors (as in Rust, but perhaps in a less refined
way).
Bye,
bearophile
H. S. Teoh:
How do you implement a completely GC-free AA with no limit on
number of entries stored?
Ada2012 has a fixed-size hash in the standard library, it can
even be allocated on the stack. But the number of entries is not
unlimited.
Bye,
bearophile
Jonathan:
This is not intended. Note that calling "return;" after
"funi(...)" makes everything work. However, it feels like I'm
doing something wrong here?
Try:
enum RunOpt { opt1, opt2, opt3 } // No semicolon here
final switch (option) with (RunOpt) {
case opt1: fun1(...); break;
Marc Schütz:
"Functions declared as abstract can still have function bodies.
This is so that even though they must be overridden, they can
still provide ‘base class functionality.’"
=> it's intentional
But also they can not have.
I don't think it's intentional. I think it's a temporary
lim
Daniel Kozak:
You can just use min:
import std.stdio, std.algorithm;
struct Thing {
uint x;
alias x this;
}
alias minimum = reduce!min;
void main() {
immutable ar1 = [10, 20, 30, 40, 50];
ar1.minimum.writeln;
immutable ar2 = [Thing(10), Thing(20), Thing(40)];
ketmar:
But I think the "j = x.byKey.front; p = x.byValue.front;"
code looks sufficiently idiomatic, and its performance is
terrible.
that's why i suggest to extend AA API, adding x.firstKey and
x.firstValue functions. i'll try to make the patch soon.
In theory the best solution is to impr
It seems fit for a performance bug report. I have to create a
synthetic benchmark that shows just the problem.
https://issues.dlang.org/show_bug.cgi?id=13410
(Perhaps I have credited the wrong person there, sorry, I will
fix).
Bye,
bearophile
ketmar:
Thank you for your analysis and code.
while (x.length) {
foreach (key; x.keys) {
auto pp = key in x;
if (pp is null) continue;
j = key;
p = *pp;
x.remove(j);
This is a little cleaner:
while (x.lengt
Charles:
My solution I came up with (and works locally) is:
import std.stdio;
void main() {
int height=1,t=1,oldN=0,n;
readf(" %d\n", &t);
foreach (i;0 .. t) {
readf(" %d\n", &n);
foreach (j; oldN .. n)
I suggest to add a blank line after the import, to move t
Adam D. Ruppe:
If you want to compare the runtime type of a class object, you
can do:
if(typeid(obj_one) == typeid(obj_two))
that should tell you if they are the same dynamic class type.
And what about:
if (is(typeof(obj_one) == typeof(obj_two)))
Bye,
bearophile
This is C++ code that solves one Euler problem:
--
#include
#include
const unsigned int H = 9, W = 12;
const int g[6][3] = {{7, 0, H - 3},
{1 + (1 << H) + (1 << (2 * H)), 0, H - 1},
{3 + (1 << H), 0, H - 2},
{3 + (2 <<
Ali Çehreli:
Unless there is a specific reason not to, use 'string'. When
you really need random access to characters, then use 'dstring'.
So are the use cases for wstring limited?
Bye,
bearophile
nikki:
I use it to change my d sourcefile slightly (into valid
markdown)
then I use a node module (ghmd) to make sortof sexy html from
that.
Are you going to add popups of the types as in the F# page I have
linked?
Bye,
bearophile
rcor:
I've tried to express my problem in a mostly minimal example
here:
https://gist.github.com/murphyslaw480/d4a5f857a104bcf62de1
The class Point has an alias this to its own property
'feature()', which returns a reference to a private member.
When I try to sort a Point[], DMD fails with "
nikki:
I've been googling without luck, is there a way to do literate
programming in D?
D1 had built-in support for literate programming, but it was
removed from D2 because it was regarded as not useful enough:
http://digitalmars.com/d/1.0/html.html
I find literate Haskell programs all the
maik klein:
Are there any exercises/challenges for D?
Some exercises here:
http://rosettacode.org/wiki/Reports:Tasks_not_implemented_in_D
Please announce them here when you solve some of them :-)
Bye,
bearophile
Jeremy DeHaan:
It compiles if I remove the 'if(typeof(T) is dchar)' section.
Any thoughts?
Try:
if (is(T == dchar))
Bye,
bearophile
Oleg B:
[code]
void doSome(size_t N, T, string AS)( vec!(N,T,AS) v ) { }
struct vec(size_t N, T, string AS) { T[N] data; }
void main() { doSome( vec!(3,float,"xyz")([1,2,3]) ); }
[/code]
compile with new dmd v2.066.0 and get error:
Error: template opbin.doSome(ulong N, T, string AS)(vec!(N, T,
Aerolite:
I was surprised to learn yesterday that D does not actually
support Multiple-Dispatch, also known as Multimethods. Why is
this? Support for this feature is already present in Scala, C#
4.0, Groovy, Clojure, etc... Would it not make sense for D to
remain competitive in this regard?
I
Ola Fosheim Grøstad:
Bearophile has created many such examples at Rosettacode.
I am updating and improving them, but I have created only a
percentage of them (60-70%? I don't know).
Bye,
bearophile
maik klein:
Are there any exercises/challenges for D?
Something like this?
http://www.haskell.org/haskellwiki/99_questions/1_to_10
This is an interesting question. There are many
exercises/challenges that can be done in D, but I don't know any
specific for D. As D challenge I suggest to wr
ketmar:
so it can be forgotten in Bugzilla. ;-)
And in ten, or one hundred or one thousand years the whole D
language will be forgotten. There are various levels of
remembering and forgetting. Putting bugs and ERs in databases is
a different kind of forgetting.
Bye,
bearophile
ketmar:
but i tend not to fill enhancement requests without
corresponding patches,
I agree that having a patch ready is much better. But people like
me file hundreds of ERs without too much damage done, and many of
them get eventually implemented. If you find a D limitation, then
putting th
ketmar:
there is currenly no way to specify attributes for such implicit
delegates.
It could be a nice language enhancement.
Bye,
bearophile
Bienlein:
@nogc is meant mostly for stack-allocation.
Ah, I missed that. Thanks for telling me.
@nogc is also for allocation from the C heap, despite this is
less common :-)
Bye,
bearophile
jicman:
This is line 7634:
const Size DEFAULT_SCALE = { 5, 13 };
What does the error say and how can I fix it? Thanks.
Can you show the (reduced) definition of Size and DEFAULT_SCALE?
Even better to show a minimized self-contained program that has
the problem.
Bye,
bearophile
Bienlein:
Is there a way to get around this?
Perhaps there are ways, but note that @nogc is meant mostly for
stack-allocation.
In general when in D you have to write lot of hairy code to do
something, it means that in most cases you shouldn't do that
something.
When calling delete t the
ketmar:
don't use '==' to check for nulls. the right way is:
if (foo is null) {}
if (bar !is null) {}
'==' transforms to opEquals call (see 'operator overloading')
and 'is' not.
I use "is" and "!is" for class references and == != for pointers.
But now I think you are right, and in D it
nikki:
How would you write it?
I don't know how much idiomatic this is, but you can start
cleaning up the code:
- Renaming the function with something more clear;
- using a D enumeration for the various constants.
- I have used a "." before the module-level variables to denote
better they a
Suliman:
bool[4] x = [1, 1, 0, 0];
BitArray ba = BitArray(x);
When I try to compile this I am getting error:
source\app.d(13): Error: cannot implicitly convert expression
(x) of type bool[4] to uint
What I am doing wrong?
It still lacks some features like a constructor that accepts a
(l
Marc Schütz:
But it would need to halt the system of course, because
throwing a RangeError might not work in his minimalistic
environment.
Halting the system, or jumping to a error routine seems better
than running in undefined state.
Bye,
bearophile
Suliman:
foreach (field; result.tupleof)
Why I should here specify type of iterable element, but not
first element that I use for iteration?
I mean:
foreach (_some_type_possible_enum_ field; result)
?
I don't understand your question. In my code I have not specified
types in the foreach
Suliman:
void main()
{
auto result = readconfig();
foreach (_; result)
{
// I want to iterate result that I got from structure.
}
}
auto readconfig()
{
struct ConfigStruct
{
string key1;
st
nrgyzer:
Sure, I can also use nested functions, but in my opinion it
results in dirty and complex code. It's totally overkilled
compared to a simple if and goto-instruction.
Often nested functions are less complex, more clean and simpler
code compared to using gotos. I suggest to start using
It looks like a compiler bug
https://issues.dlang.org/show_bug.cgi?id=13321
Bye,
bearophile
nrgyzer:
import std.bigint;
void main(string[] args)
{
BigInt i = "12345";
if (args.length > 1)
{
goto Exit;
}
i = BigInt("67890");
Exit:
return;
}
When I try to compile this sample application I'm getting the
foll
H. S. Teoh:
Is there a bug filed for this?
Probably there is. But I stopped filing similar bugs because they
seem to have a very low priority.
Bye,
bearophile
ketmar:
other function declarations (methods, nested functions) accepts
'static', so why free functions shouldn't?
For various reasons, one of them is that accepting useless code
confuses newbies and doesn't allow them to build a correct model
of the D semantics in their head.
Bye,
bearoph
Nordlöw:
I'm missing an instantiator function for std.typecons:Nullable.
Is this is intentional? If not, is this
Nullable!T nullable(T)(T a)
{
return typeof(return)(a);
}
sufficient for our needs?
It could be sufficient, but note that in Phobos there are two
different versions of Nulla
safety0ff:
Here's a candidate for
http://rosettacode.org/wiki/Extensible_prime_generator#D in
case it is preferred to the existing entry:
http://dpaste.dzfl.pl/43735da3f1d1
I was away. I have added your nice code with some small changes
as an alternative faster version. I think you have com
Théo Bueno:
Same issue here with dsfml-audio, this is really annoying :/
Have you filed the issue?
Bye,
bearophile
Marc Schütz:
Isn't SuperFastHash vulnerable to collision attacks?
D AAs used to be not vulnerable to collision attacks because they
resolved collisions building a red-black tree for each bucket.
Later buckets became linked lists for speed, leading to the
current sensitivity to collision att
TJB:
I am trying to find the max and min values in an associative
array. Say I have:
double[char] bids;
bid['A'] = 37.50;
bid['B'] = 38.11;
bid['C'] = 36.12;
How can I find the max and min values. I am thinking that I
need to use max and min functions from std.algorithm, but not
sure how to
Freddy:
uint[uint] test;
void main(){
test=[0:2 ,1:3 ,2:4];
writeln(test.map!(a=>a-2));
}
If you need keys or values you have .keys .values, .byKey,
.byValue (the first two are eager). If you need both you are out
of luck, and if you want to write safe code it's better to us
Eric:
Thanks. That really works. I timed doing
auto mySlice = ptr1[0 .. ptr2 - ptr1]; 1,000,000 times
versus
auto mySlice = ptr1[0 .. ptr2 - ptr1].dup; 1,000,000 times
and I am quite convinced the data is not being copied.
Take a look at the asm!
Bye,
bearophile
H. S. Teoh:
OK, makes sense. But what about if only the most significant
bit is 1?
Wouldn't that also be an overflow? So you're essentially
checking if the
topmost n bits are zero, where n is the number of bits you wish
to shift by.
Of course.
https://issues.dlang.org/show_bug.cgi?id=13231
Eric:
Suppose I have some memory allocated on the heap, and I have
two pointers pointing to the beginning and end of a contiguous
segment
of that memory. Is there a way I can convert those two pointers
to an array slice without actually copying anything within the
segment?
Use something li
Marc Schütz:
class buffer(T, size_t sz) {
auto arr = new T[sz];
This allocates an array with `sz` elements once _at compile
time_, places it somewhere into the executable, and uses its
address as the default initializer for the member `arr`.
Right. It's not a compiler bug. Dmd/ldc
H. S. Teoh:
What would you check for? Shifting something that already has
its high bit set?
If you have a uint where the 3 most significant bits are 1, and
you shift it 3 bits on the left, you lose those three bits, you
have an overflow. The point of checkedint functions/intrinsics is
to re
Is it a good idea to add int/uint/long/ulong functions for the
"<<" left shift operation here?
https://github.com/D-Programming-Language/druntime/blob/master/src/core/checkedint.d
Bye,
bearophile
Kozzi11:
Is possible to somehow split class declaration and definition.
I mean something like this:
class C
{
void hello(); // just prototype
}
class C
{
void hello()
{
//actual code
}
}
or something like this
void C.hello() {
//actual code
}
I think this is cur
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