Re: Is `void` the correct way to say "do not initialize this variable"?
On 10/3/22 02:30, ryuukk_ wrote: I have tried to look at the documentation and various places on the DMD source, but i couldn't find the answer https://dlang.org/spec/declaration.html#void_init ```D MyStruct test = void; ``` Does this guarantee that the compiler will not initialize it? Yes Does it work with static arrays of struct too? It works but not as someone could expect. In case of ``` Foo[2] arr = void; ``` `arr` value is not defined, it is not an initialized array of uninitialized elements like you want, it is just uninitialized array. The generated code is different than ``MyStruct test;`` What exactly (by exactly i mean is the behavior documented somewhere?) ``void`` does?
Re: Is `void` the correct way to say "do not initialize this variable"?
I got the answer thanks to IRC chat: https://dlang.org/spec/declaration.html#void_init
Is `void` the correct way to say "do not initialize this variable"?
I have tried to look at the documentation and various places on the DMD source, but i couldn't find the answer ```D MyStruct test = void; ``` Does this guarantee that the compiler will not initialize it? Does it work with static arrays of struct too? The generated code is different than ``MyStruct test;`` What exactly (by exactly i mean is the behavior documented somewhere?) ``void`` does?
Re: csvReader: how to read only selected columns while the class Layout has extra field?
On 10/2/22 23:18, mw via Digitalmars-d-learn wrote: A CSV library should consider all the use cases, and allow users to ignore certain fields. Filed issue: https://issues.dlang.org/show_bug.cgi?id=23383 Let's see what others have to say.
Re: Visual D doesn't work, now Visual Studio Code / D doesn't work!!!! ....
Visual Studio with its c++ components can debug D code, it should not require Visual D to do so. Open executable as project. If this does not work, you have a serious issue in your system/VS install. This may help to narrow down what is going on.
Re: csvReader: how to read only selected columns while the class Layout has extra field?
On Sunday, 2 October 2022 at 21:03:40 UTC, rassoc wrote: But say, I'm curious, what's the purpose of adding an optional/useless contents field? What's the use-case here? We have a class/struct for a data record, some of its data fields need to be saved/loaded from CSV files; while there are other helper fields which are useful for various computation tasks (e.g. caching some intermediate computation results), these fields do not need to be saved/loaded from the csv files. A CSV library should consider all the use cases, and allow users to ignore certain fields.
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 18:24:51 UTC, Ali Çehreli wrote:
On 10/2/22 10:55, data pulverizer wrote:
> ```
> this(T)(ref return scope T original)
> if(is(T == RVector!(Type)))
> {
> //... code ...
> }
> ```
I've just tested. That is used only for explicit constructor
syntax:
auto b = RVector!int(a);// templatized
>
>
> But this now works:
>
>
> ```
> this(ref return scope RVector!(Type) original)
> {
> //... code ...
> }
> ```
That one works for both syntaxes:
auto b = RVector!int(a);// templatized
auto c = a; // non-templatized
Certainly confusing and potentially a bug... :/
It's a bug in the documentation.
https://issues.dlang.org/show_bug.cgi?id=23382
https://github.com/dlang/dlang.org/pull/3427
Re: csvReader: how to read only selected columns while the class Layout has extra field?
On 10/2/22 21:48, mw via Digitalmars-d-learn wrote:
```
text.csvReader!Layout(["b","c","a"]); // Read only these column
```
The intention is very clear: only read the selected columns from the csv, and
for any other fields of class Layout, just ignore (with the default D .init
value).
Here's why it's not currently working:
"An optional header can be provided. The first record will be read in as the header.
If Contents is a struct then the header provided is expected to correspond to the fields
in the struct."
"expected to correspond" means that the number of fields in the content struct
can't exceed the header element count as you can see in the actual code [1]:
```
foreach (ti, ToType; Fields!(Contents))
{
if (indices[ti] == colIndex) // indices.length depends on passed in
colHeaders.length
...
}
```
The current index exception is bad, this needs an assert in the constructor
with a nicer error message.
But say, I'm curious, what's the purpose of adding an optional/useless contents
field? What's the use-case here?
[1]
https://github.com/dlang/phobos/blob/8e8aaae5080ccc2e0a2202cbe9778dca96496a95/std/csv.d#L1209
Re: csvReader: how to read only selected columns while the class Layout has extra field?
``` text.csvReader!Layout(["b","c","a"]); // Read only these column ``` The intention is very clear: only read the selected columns from the csv, and for any other fields of class Layout, just ignore (with the default D .init value).
csvReader: how to read only selected columns while the class Layout has extra field?
Hi,
I'm following the example on
https://dlang.org/phobos/std_csv.html
```
class Layout
{
int value;
double other;
string name;
int extra_field; // un-comment to see the error
}
void main()
{
import std.csv;
import std.stdio: write, writeln, writef, writefln;
import std.algorithm.comparison : equal;
string text = "a,b,c\nHello,65,2.5\nWorld,123,7.5";
auto records =
text.csvReader!Layout(["b","c","a"]); // Read only these
column
foreach (r; records) writeln(r.name);
}
```
This works fine so far, but if I un-comment the extra_field line,
I got runtime error:
```
core.exception.ArrayIndexError@/dlang/dmd/linux/bin64/../../src/phobos/std/csv.d(1209):
index [3] is out of bounds for array of length 3
??:? _d_arraybounds_indexp [0x5565b4b974d1]
/dlang/dmd/linux/bin64/../../src/phobos/std/csv.d:1209 pure @safe
void std.csv.CsvReader!(onlineapp.Layout, 1, immutable(char)[],
dchar, immutable(char)[][]).CsvReader.prime() [0x5565b4b73ed2]
/dlang/dmd/linux/bin64/../../src/phobos/std/csv.d:1154 pure @safe
void std.csv.CsvReader!(onlineapp.Layout, 1, immutable(char)[],
dchar, immutable(char)[][]).CsvReader.popFront() [0x5565b4b73c80]
/dlang/dmd/linux/bin64/../../src/phobos/std/csv.d:1069 pure ref
@safe std.csv.CsvReader!(onlineapp.Layout, 1, immutable(char)[],
dchar, immutable(char)[][]).CsvReader
std.csv.CsvReader!(onlineapp.Layout, 1, immutable(char)[], dchar,
immutable(char)[][]).CsvReader.__ctor(immutable(char)[],
immutable(char)[][], dchar, dchar, bool) [0x5565b4b73ae8]
/dlang/dmd/linux/bin64/../../src/phobos/std/csv.d:366 pure @safe
std.csv.CsvReader!(onlineapp.Layout, 1, immutable(char)[], dchar,
immutable(char)[][]).CsvReader
std.csv.csvReader!(onlineapp.Layout, 1, immutable(char)[],
immutable(char)[][], char).csvReader(immutable(char)[],
immutable(char)[][], char, char, bool) [0x5565b4b735f3]
./onlineapp.d:18 _Dmain [0x5565b4b72ca4]
```
I'm just wondering how to work-around this?
Thanks.
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 18:24:51 UTC, Ali Çehreli wrote: I've just tested. That is used only for explicit constructor syntax ... Many thanks. Knowledgeable as always!
Re: Stop writeln from calling object destructor
On 10/2/22 10:55, data pulverizer wrote:
> On Sunday, 2 October 2022 at 17:28:51 UTC, data pulverizer wrote:
>> Sorry I'll need to implement all the overloaded copy constructors and
>> see if that fixes it.
>
> I've got it, something weird happened to my copy constructor. This was
> my original attempt and was ignored (didn't run in the copy constructor):
>
> ```
> this(T)(ref return scope T original)
> if(is(T == RVector!(Type)))
> {
> //... code ...
> }
> ```
I've just tested. That is used only for explicit constructor syntax:
auto b = RVector!int(a);// templatized
>
>
> But this now works:
>
>
> ```
> this(ref return scope RVector!(Type) original)
> {
> //... code ...
> }
> ```
That one works for both syntaxes:
auto b = RVector!int(a);// templatized
auto c = a; // non-templatized
Certainly confusing and potentially a bug... :/
> No idea why. `Type` is a template parameter of the object.
Minor convenience: You can replace all RVector!(Type) with just RVector
in the implementation of RVector because the name of the struct template
*is* that specific instantiation of it:
struct RVector(Type) {
// RVector below means RVector!Type:
this(ref return scope RVector original)
{
// ...
}
}
Ali
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 17:51:59 UTC, Ali Çehreli wrote: What I noticed first in your original code was that it would be considered buggy because it was not considering copying. Every struct that does something in its destructor should either have post-blit (or copy constructor) defined or simpler, disallow copying altogether. Thanks for the advice, for a while now I didn't know what was creating the issue. The code I'm running is my D connector to the R API and for ages I didn't know where the multiple destructor calls to allow an object to be garbage collected by the R API was coming from, and it was breaking the whole thing. I think I'll have to play it by ear whether to disable the copy constructor altogether or to use it now it is working. Thanks both of you.
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 17:28:51 UTC, data pulverizer wrote:
Sorry I'll need to implement all the overloaded copy
constructors and see if that fixes it.
I've got it, something weird happened to my copy constructor.
This was my original attempt and was ignored (didn't run in the
copy constructor):
```
this(T)(ref return scope T original)
if(is(T == RVector!(Type)))
{
//... code ...
}
```
But this now works:
```
this(ref return scope RVector!(Type) original)
{
//... code ...
}
```
No idea why. `Type` is a template parameter of the object.
Re: Stop writeln from calling object destructor
On 10/2/22 10:28, data pulverizer wrote:
> On Sunday, 2 October 2022 at 17:19:55 UTC, data pulverizer wrote:
>> Any reason why this could be?
>
What I noticed first in your original code was that it would be
considered buggy because it was not considering copying. Every struct
that does something in its destructor should either have post-blit (or
copy constructor) defined or simpler, disallow copying altogether.
That's what I did here:
https://github.com/acehreli/alid/blob/main/cached/alid/cached.d#L178
@disable this(this);
I think disabling copy constructor was unnecessary but I did that as well:
@disable this(ref const(typeof(this)));
The issue remains and bothers me as well. I think writeln copies objects
because D disallows references to rvalue. We couldn't print rvalues if
writeln insisted on 'ref'. Or, rvalues would be copied anyway if we used
'auto ref'. Hence the status quo...
> Sorry I'll need to implement all the overloaded copy constructors and
> see if that fixes it.
The best solution I know is to disable copying and printing not the
object but an explicit string representation of it:
Added:
@disable this(this);
Added (there are better ways of doing the same e.g. using a 'sink'
parameter):
string toString() const {
import std.format : format;
return format!"id: %s"(id);
}
Called toString:
writeln("MyObject: ", obj.toString);
Ali
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 17:19:55 UTC, data pulverizer wrote: Any reason why this could be? Sorry I'll need to implement all the overloaded copy constructors and see if that fixes it.
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 16:44:25 UTC, Paul Backus wrote: It's because `writeln` is copying the object, and each of the copies is being destroyed. If you add a copy constructor to your example, you can see it happening: ... I thought something like this could be happening in my original implementation and tried implementing a copy constructor using this reference https://dlang.org/spec/struct.html#struct-copy-constructor but it did not work. Both your's and the manual's suggestion works for my baby example but not for my actual code. Any reason why this could be?
Re: Stop writeln from calling object destructor
On Sunday, 2 October 2022 at 16:21:47 UTC, data pulverizer wrote:
I've noticed that `writeln` calls the destructor of a struct
multiple times and would like to know how to stop this from
happening.
It's because `writeln` is copying the object, and each of the
copies is being destroyed. If you add a copy constructor to your
example, you can see it happening:
```d
import std.stdio: writeln;
struct MyObject
{
int id;
this(int id) @nogc
{
this.id = id;
}
this(inout ref MyObject) inout
{
writeln("Object copy constructor...");
}
~this()
{
writeln("Object destructor ...");
}
}
void main()
{
auto obj = MyObject(42);
writeln(obj);
writeln("Goodbye:\n");
}
```
Output:
```d
Object copy constructor...
Object copy constructor...
Object copy constructor...
Object copy constructor...
MyObject(0)Object destructor ...
Object destructor ...
Object destructor ...
Object destructor ...
Goodbye:
Object destructor ...
```
Stop writeln from calling object destructor
I've noticed that `writeln` calls the destructor of a struct
multiple times and would like to know how to stop this from
happening. It has become a very serious problem when working with
objects that have memory management external to D.
Here is a repeatable example, where the destructor appears to
have been called 4 times with one call of `writeln` before the
object actually goes out of scope:
Code:
```
import std.stdio: writeln;
struct MyObject
{
int id;
this(int id) @nogc
{
this.id = id;
}
~this()
{
writeln("Object destructor ...");
}
}
void main()
{
auto obj = MyObject(42);
writeln("MyObject: ", obj);
writeln("Goodbye:\n");
}
```
Output:
```
$ rdmd gc.d
MyObject: MyObject(42)Object destructor ...
Object destructor ...
Object destructor ...
Object destructor ...
Goodbye:
Object destructor ...
```
Thank you
Re: D installer
On Sunday, 2 October 2022 at 12:37:37 UTC, Mike Parker wrote: On Sunday, 2 October 2022 at 11:33:47 UTC, Imperatorn wrote: I only have Visual Studio 2022. Will the installer be updated to support that or am I missing some components?  You should be fine. Select the bottom option since you already have it installed. Thanks for a quick reply!
Re: Visual D doesn't work, now Visual Studio Code / D doesn't work!!!! ....
On Sunday, 2 October 2022 at 11:00:06 UTC, Daniel Donnell, Jr wrote: I thought I set everything up correctly, and now: ``` Exception thrown at 0x7FF7D6E2E230 in metamath-d.exe: 0xC096: Privileged instruction. Unable to open natvis file 'c:\Users\fruit\.vscode\extensions\webfreak.code-d-0.23.2\dlang-debug\dlang_cpp.natvis'. ``` So what the hell do you D developers use to code with if A) Visual D doesn't work - it just ate my app.obj file and can't find it anymore no matter if I clean or re-order the executable paths in settings. B) VS Code doesn't work out-of-the-box. Every. Single. Time I get around to using D, there's always something that pops up and doesn't work right. And it never gets fixed. How the heck do you expect me to debug without a proper debugging IDE :| Plenty of people are using Visual D and VS Code with D. Whatever the source of your problem, it's surely fixable. Though if no one has encountered this particular issue, then it may take some doing to figure out the problem. I've emailed Rainer, the maintainer of Visual D, to notify him of this thread. He might have an idea of what's wrong, or at least will be in a position to ask more informed questions than I or others to help you solve the problem. In the future, when you encounter Visual D issues, please post in the IDEs forum. Rainer checks in there more regularly and will be more likely to see your posts. https://forum.dlang.org/group/ide
Re: D installer
On Sunday, 2 October 2022 at 11:33:47 UTC, Imperatorn wrote: I only have Visual Studio 2022. Will the installer be updated to support that or am I missing some components?  You should be fine. Select the bottom option since you already have it installed.
Re: Visual D doesn't work, now Visual Studio Code / D doesn't work!!!! ....
On Sunday, 2 October 2022 at 11:00:06 UTC, Daniel Donnell, Jr wrote: I thought I set everything up correctly, and now: ``` Exception thrown at 0x7FF7D6E2E230 in metamath-d.exe: 0xC096: Privileged instruction. Unable to open natvis file 'c:\Users\fruit\.vscode\extensions\webfreak.code-d-0.23.2\dlang-debug\dlang_cpp.natvis'. ``` So what the hell do you D developers use to code with if A) Visual D doesn't work - it just ate my app.obj file and can't find it anymore no matter if I clean or re-order the executable paths in settings. B) VS Code doesn't work out-of-the-box. Every. Single. Time I get around to using D, there's always something that pops up and doesn't work right. And it never gets fixed. How the heck do you expect me to debug without a proper debugging IDE :| Did you try DlangIDE or Dexed? They could be a solution
D installer
I only have Visual Studio 2022. Will the installer be updated to support that or am I missing some components?  Thanks!
Re: bigint and pow
On 10/2/22 09:24, Fausto via Digitalmars-d-learn wrote:
Thanks a lot. I am to used to C and, more important, I didn't think to look for
also another operator for the power function :)
Oh, and I forgot to mention that this is doing what you probably asked for
originally:
```d
import std;
import cmath = core.stdc.math;
void main()
{
// both print 1e+72
writeln(pow(10.0, 72));
writeln(cmath.pow(10, 72));
}
```
But it's just floating-point scientific notation, not true BigInts.
Another math difference from C is that D has well-defined wrapping math for
signed ints.
Re: bigint and pow
On 10/2/22 09:24, Fausto via Digitalmars-d-learn wrote:
Thanks a lot. I am to used to C and, more important, I didn't think to look for
also another operator for the power function :)
D does have pow and many other useful math functions [1], it's just not defined
for BitInts. Oh, and speaking of C, you also have access to all the usual C
math [1] functions with just an import:
```d
import std.stdio : writeln;
void main()
{
import std.math : pow;
writeln(pow(10, 3)); // pow from D
import core.stdc.math : pow;
writeln(pow(10, 3)); // pow from C
// can also make it more explicit to show where it is coming from:
import cmath = core.stdc.math;
writeln(cmath.pow(10, 3));
}
```
Have fun with D!
[1] https://dlang.org/library/std/math.html
[2] https://dlang.org/library/core/stdc/math.html
Re: What are best practices around toString?
On Saturday, 1 October 2022 at 17:50:54 UTC, tsbockman wrote: but unless it is provided with a good estimate of the final length at the beginning, it will allocate several times for a longer string, and the final buffer will be, on average, 50% larger than needed. I see, it's smart! SDB@79
Re: Interfacing with basic C++ class
On Friday, 30 September 2022 at 22:56:06 UTC, Ogi wrote: On Thursday, 29 September 2022 at 12:49:06 UTC, Riccardo M wrote: When interfacing to C++, disregard the keyword and look at the implementation instead. If all its member functions are non-virtual, map it to struct. Otherwise map it to class. If it defines at least one pure virtual member function, map it to abstract class. If all its member functions are either pure virtual or non-virtual and it contains no fields, map it to interface. Sounds complicated? Well, that’s because C++ is complicated. Ok, in layman terms, is it correct to say that I should match the underlining structure of the object (e.g in terms of vtbl) so that C++ side and D side can work with each other correctly? In C++, member functions defined inside its class are called *inline* member functions. In contrast to normal functions which must be defined once and only once in your program, inline functions must be defined in every translation unit that uses them. Let’s replicate your linking error in C++: Well, I didn't know the implications of inlining member functions: basically when a member function is inlined, it has no linkage so I am pretty much done with using D in such case. While in C++ you can import the header and call the member function anyway. The only solution would be reimplementing the offending function on D side.
Re: bigint and pow
On Sunday, 2 October 2022 at 02:02:37 UTC, rassoc wrote:
On 10/2/22 00:04, Fausto via Digitalmars-d-learn wrote:
Hello,
I am trying to use pow with an integer argument, but I cannot
have a bigint result, for example, ```pow(10,72)```.
Do I have to write my pow function or is there a native
solution?
thanks,
Fausto
In contrast to certain scripting languages, there's no implicit
promotion, you have to opt in for BigInt [1] usage in D:
```d
import std;
void main()
{
// all print the same
writeln(BigInt(10) ^^ 72);
writeln(10.BigInt ^^ 72);
writeln("10".BigInt ^^ 72);
}
```
[1] https://dlang.org/phobos/std_bigint.html#.BigInt
Thanks a lot. I am to used to C and, more important, I didn't
think to look for also another operator for the power function :)
