Re: const of AliasSeq is silently ignored
On 04/08/2019 12:56 PM, Yuxuan Shui wrote: In this example: const(AliasSeq!(int, int)) a; I would expect that to mean a type list (int, int) that cannot be modified, meaning that it is not allowed to change it from (int, int). pragma(msg, typeof(a)); // (int, int) Makes sense to me. However, there is no syntax that allows mutating an AliasSeq. In other words, the following doesn't compile anyway: AliasSeq!(int, int) a; a ~= AliasSeq!(double); So, adding const to that construct does not add any meaning but not many people would notice it. :) Ali
Re: Overloads not returning appropriate info. [Field reflunkory]
On Saturday, 6 April 2019 at 12:20:28 UTC, Alex wrote: Error: variable `std.traits.ParameterDefaults!(foo).Get!1u.Get` only parameters or stack based variables can be `inout` so i think that is a bug in the phobos library see: https://forum.dlang.org/thread/qbqvkcoexxtlvlxob...@forum.dlang.org
Re: Overloads not returning appropriate info. [Field reflunkory]
On 4/8/2019 7:39 AM, Alex wrote: My point is that you are going ape shit over using T.stringof, you posted no I mean, half the shit in __traits looks like it could be in std.traits and there Please tone down both the aggressiveness and the use of cuss words, and use professional demeanor.
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 18:04:28 UTC, kdevel wrote:
On Sunday, 7 April 2019 at 17:16:12 UTC, Seb wrote:
---
["a": 1].byPair.array.sort!((a, b) => a.value <
a.value).release.each!writeln;
---
What's the purpose of .release? The documentation in
https://dlang.org/phobos/std_range.html#.SortedRange.release is
rather monosyllabic.
As others have already explained, you'll get the original range
back (instead of the SortedRange).
Sometimes, this is useful.
The obvious example is assigning back to the original range:
---
import std.experimental.all;
void main()
{
auto arr = ["a": 1].byPair.array;
arr = arr.sort!((a, b) => a.value < a.value);
}
---
https://run.dlang.io/is/8sFxVb
OTOH this works:
---
import std.experimental.all;
void main()
{
auto arr = ["a": 1].byPair.array;
arr = arr.sort!((a, b) => a.value < a.value).release;
}
---
https://run.dlang.io/is/TgXUZj
In the example where I used it, you won't need it.
Sorry for the confusion, but as it's often every now and then
pretty useful, I thought it is a nice idea to give it more
spotlight as it's one of the lesser known parts of Phobos.
Re: I really don't understand DUB
On Monday, 8 April 2019 at 19:54:28 UTC, WhatMeWorry wrote: Now, I've studied the on-line documentation and even walked through the code somewhat but I'm not making an headway. Very relatable. My tips so far are: - Look for projects in github with a similar structure to yours and look at their package files. Want to split up your library in sub-components? Look at: https://github.com/d-gamedev-team/gfm/blob/master/dub.json or: https://github.com/AuburnSounds/Dplug/blob/master/dub.json Want to build a game on Windows without console, with and icon and including Dll's? https://github.com/gecko0307/dagon-demo/blob/master/dub.json - If you think "okay, my D project is slightly unconventional, but I think I can make it work with dub using the right configuration / preBuildCommands / targetType none": It's an uphill battle, it won't work well (or at all). - bookmark the package reference (https://dub.pm/package-format-json.html), you'll go back to it a lot. (Surely it hurts that I've never been exposed to a library or package manager in general) It shouldn't be this hard to grasp. Is there some good beginner tutorial that I'm missing? Nope. I considered writing one, but the prerequisite of that is that I understand dub myself. You'll have to do with: https://dub.pm/getting_started.html https://dub.pm/advanced_usage.html https://github.com/dlang/dub/wiki/Cookbook
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 19:43:11 UTC, Julian wrote:
On Monday, 8 April 2019 at 19:29:33 UTC, 4544fa8d wrote:
It's really not possible to call functions in modules like in
any other languages? :S
What some other languages do is collect all of those calls into
an
implicit function that's called before main(). What D does is
run
that code at compile-time.
Another way, from https://dlang.org/spec/module.html#staticorder
In thisexe.d:
import std.stdio, std.path, std.file;
public string root_dir;
shared static this() {
root_dir = dirName(thisExePath());
}
In thisexe_ex.d:
#! /usr/bin/env rdmd
import thisexe, std.stdio;
void main() {
writeln(root_dir);
}
does what you'd expect.
const of AliasSeq is silently ignored
In this example: const(AliasSeq!(int, int)) a; pragma(msg, typeof(a)); // (int, int) This kind of make sense, since AliasSeq is not a "single" type. But silently dropping const seems bad, the compiler should probably report an error/warning in this case?
I really don't understand DUB
I've been using DUB for several years and I've gotten it to work generally. But I've been trying to troubleshoot a DUB issue for two days now and I've come to the conclusion, I don't really understand DUB and I'm tired of muddling through. (Surely it hurts that I've never been exposed to a library or package manager in general) Now, I've studied the on-line documentation and even walked through the code somewhat but I'm not making an headway. Maybe a higher level approach is required. Is there some good beginner tutorial that I'm missing? Ideally, like a gentle walk through, for both Windows and POSIX?
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 18:04:28 UTC, kdevel wrote: What's the purpose of .release? The documentation in https://dlang.org/phobos/std_range.html#.SortedRange.release is rather monosyllabic. The sort function returns a SortedRange, which is usually an array wrapper with the extra type information that its content is sorted, enabling certain algorithms like lowerBound and upperBound with help of binary search. "Ranges whose elements are sorted afford better efficiency with certain operations. For this, the assumeSorted function can be used to construct a SortedRange from a pre-sorted range. The std.algorithm.sorting.sort function also conveniently returns a SortedRange. SortedRange objects provide some additional range operations that take advantage of the fact that the range is sorted." (https://dlang.org/phobos/std_range.html) When you release it, you get it back as a normal slice without the type information that it is sorted, so you can assign it to regular old array variables. As mentioned in the quote, you can get it back as sortedRange with assumeSorted.
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 19:29:33 UTC, 4544fa8d wrote:
It's really not possible to call functions in modules like in
any other languages? :S
What some other languages do is collect all of those calls into an
implicit function that's called before main(). What D does is run
that code at compile-time. Silly example:
import std.stdio;
T twice(T)(T n) { return 2 * n; }
auto x = twice(5);
void main() {
writeln(x);
}
Take a look at the compiled result: https://godbolt.org/z/8vLsv9
There's a twice() that's compiled in, but if you look at x it's
already the result of a call to twice():
int example.x:
.long 10
and the (unoptimized) main just fetches that number to print.
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 19:05:33 UTC, Julian wrote:
Shorter:
string root_dir() {
static string cache;
return cache ? cache : (cache = dirName(thisExePath()));
}
This might spam readlink() syscalls if they somehow return the
It's really not possible to call functions in modules like in any
other languages? :S
---
import std.file;
import std.path;
import std.stdio;
//const ROOT_DIR = dirName(thisExePath());
int someInt = 0;
string someString = "sfgsdgdf";
writeln("one");
void main(){
writeln("two");
}
---
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 18:54:10 UTC, Julian wrote:
@property
string root_dir() {
static string cache;
static bool isInit = false;
if (!isInit) {
isInit = true;
cache = dirName(thisExePath());
}
return cache;
}
Shorter:
string root_dir() {
static string cache;
return cache ? cache : (cache = dirName(thisExePath()));
}
This might spam readlink() syscalls if they somehow return the
empty string,
but how would that even happen...
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 18:47:42 UTC, 4544fa8d wrote:
On Monday, 8 April 2019 at 18:41:00 UTC, Adam D. Ruppe wrote:
Did you put your code inside a main() function?
I want to make constant with path to directory containing
executable. This line is above main():
-
const ROOT_DIR = dirName(thisExePath());
-
This is not allowed? :O
That would give you dmd's path, if it worked.
This is allowed:
#! /usr/bin/env rdmd
import std.stdio, std.path, std.file;
@property
string root_dir() {
static string cache;
static bool isInit = false;
if (!isInit) {
isInit = true;
cache = dirName(thisExePath());
}
return cache;
}
void main() {
writeln(root_dir);
}
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 18:38:58 UTC, 4544fa8d wrote:
Hello,
I have "hello world" application. I imported std.file, executed
thisExePath() and now I have this error:
dmd -m64 -of=../../bin/manager -release ./src/manager.d
/usr/include/dmd/phobos/std/file.d(3252): Error: readlink
cannot be interpreted at compile time, because it has no
available source code
/usr/include/dmd/phobos/std/file.d(3253):called from
here: delegate () => readlink(linkz.ptr(), & buffer, 2048LU)()
/usr/include/dmd/phobos/std/file.d(3433):called from
here: readLink("/proc/self/exe")
./src/manager.d(8):called from here: thisExePath()
./src/manager.d(8):called from here:
dirName(thisExePath())
makefile:2: recipe for target 'all' failed
Whats going on? Why I cant build my executable file?
The error message is telling you that dmd is trying to run
readlink
at compile-time. But this is probably an extern (C) symbol that
isn't
resolved except by the linker to some code in libc, which can only
happen after any compile-time computation's done.
Are you trying to get the /proc/self/exe of dmd itself?
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 18:41:00 UTC, Adam D. Ruppe wrote: Did you put your code inside a main() function? I want to make constant with path to directory containing executable. This line is above main(): - const ROOT_DIR = dirName(thisExePath()); - This is not allowed? :O
Re: How to compile and link simple application?
On Monday, 8 April 2019 at 18:38:58 UTC, 4544fa8d wrote: Whats going on? Why I cant build my executable file? Did you put your code inside a main() function?
How to compile and link simple application?
Hello,
I have "hello world" application. I imported std.file, executed
thisExePath() and now I have this error:
dmd -m64 -of=../../bin/manager -release ./src/manager.d
/usr/include/dmd/phobos/std/file.d(3252): Error: readlink cannot
be interpreted at compile time, because it has no available
source code
/usr/include/dmd/phobos/std/file.d(3253):called from
here: delegate () => readlink(linkz.ptr(), & buffer, 2048LU)()
/usr/include/dmd/phobos/std/file.d(3433):called from
here: readLink("/proc/self/exe")
./src/manager.d(8):called from here: thisExePath()
./src/manager.d(8):called from here:
dirName(thisExePath())
makefile:2: recipe for target 'all' failed
Whats going on? Why I cant build my executable file?
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 17:13:32 UTC, Seb wrote: On Monday, 8 April 2019 at 08:31:33 UTC, Dennis wrote: On Monday, 8 April 2019 at 07:53:23 UTC, Robert M. Münch wrote: Why does DMD not give a hint, that an import from the standard lib might be missing? I find these explicit import statements very annyoing. There currently are a few hard-coded import hints for common functions: https://github.com/dlang/dmd/blob/master/src/dmd/imphint.d But it definitely could be better. Yeah, it's not too hard to improve this. A quick start: https://github.com/dlang/dmd/pull/9576 I can't make an issue yet, but since they're asking for a BugZilla issue, a relevant one would be "published D examples fail without import hints". In the very first chapter of the D Programming Language, library changes result in errors for enforce (which you add) and std.algorithm.splitter The book has an errata but the compiler's the very first thing that can communicate "D has helpful error messages" instead of "maybe I should wait for this language to mature a bit more". For more comprehensive hints, isn't the documentation generated? Maybe, patch docgen to generate this table as well.
Re: Iterate/sort associative array by value?
On Sunday, 7 April 2019 at 17:16:12 UTC, Seb wrote: --- ["a": 1].byPair.array.sort!((a, b) => a.value < a.value).release.each!writeln; --- What's the purpose of .release? The documentation in https://dlang.org/phobos/std_range.html#.SortedRange.release is rather monosyllabic.
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 08:31:33 UTC, Dennis wrote: On Monday, 8 April 2019 at 07:53:23 UTC, Robert M. Münch wrote: Why does DMD not give a hint, that an import from the standard lib might be missing? I find these explicit import statements very annyoing. There currently are a few hard-coded import hints for common functions: https://github.com/dlang/dmd/blob/master/src/dmd/imphint.d But it definitely could be better. Yeah, it's not too hard to improve this. A quick start: https://github.com/dlang/dmd/pull/9576
Re: Templates - What's Up with the template keyword?
On Monday, 8 April 2019 at 14:56:46 UTC, Mike Parker wrote: In the subsequent sections, I show both long and short (eponymous) forms of enum and function templates. Forgot to say... I'm typing in the examples as I go and so far I haven't been lost. Even when you don't come right out and say how to use a particular template example, I'm able to fill in the blanks and get a complete, working example.
Re: Templates - What's Up with the template keyword?
On Monday, 8 April 2019 at 14:56:46 UTC, Mike Parker wrote: You should have read further along in that chapter :-) LOL! Actually, after reading Adam's reply, I dug back into your book and I'm starting to get a reasonable handle on this. I must say, I like the slow-but-steady intro you wrote. Thanks, Mike. Great book!
Re: Templates - What's Up with the template keyword?
On Monday, 8 April 2019 at 12:23:28 UTC, Ron Tarrant wrote:
First, the question...
In Michael Parker's book, "Learning D," (Packt, 2015) on page
160 he gives an example of a basic template:
template MyTemplate(T)
{
T val;
void printVal()
{
import std.stdio : writeln;
writeln("The type is ", typeid(T));
writeln("The value is ", val);
}
}
But in "Programming in D," (self, 2009-2018) by Ali Çehreli,
there's no mention of the 'template' keyword in any of his
examples.
Has the 'template' keyword been deprecated? Or is it optional?
You should have read further along in that chapter :-) I evolve
the MyTemplate example through the end of that "Templates as code
blocks" section to this:
template MyTemplate(T) {
struct ValWrapper {
T val;
void printVal() {
import std.stdio : writeln;
writeln("The type is ", typeid(T));
writeln("The value is ", val);
}
}
}
And show that it must be instantiated like this:
void main() {
MyTemplate!int.ValWrapper vw1;
MyTemplate!int.ValWrapper vw2;
vw1.val = 20;
vw2.val = 30;
vw1.printVal();
vw2.printVal();
}
And in the next section, "Struct and class templates", I
introduce the concept of eponymous templates by rewriting
MyTemplate like so:
template ValWrapper(T) {
struct ValWrapper {
T val;
void printVal() {
writeln("The type is ", typeid(T));
writeln("The value is ", val);
}
}
}
And show that it can be instantiated with the shorthand:
ValWrapper!int vw;
And that the template can be refactored to this (since it's
eponymous):
struct ValWrapper(T) {
T val;
void printVal() {
writeln("The type is ", typeid(T));
writeln("The value is ", val);
}
}
In the subsequent sections, I show both long and short
(eponymous) forms of enum and function templates.
Re: Cannot link vibe.d sample / optlink error
On Monday, 8 April 2019 at 13:42:31 UTC, Michal Minich wrote: I used dmd 2.085.0 and 2.085.1 on Win 10 I followed sample at https://vibed.org/blog/posts/a-scalable-chat-room-service-in-d Just the beginning, where you you should compile hello word web app. command line: "dub" compilation finishes ok. then it prints "Linking..." and I get window message box: --- Unexpected OPTLINK Termination at EIP=0040F60A --- EAX=073D EBX=00438C70 ECX=0B2F EDX=038A ESI=008F EDI=073D1344 EBP=0019FF28 ESP=0019FEE0 First=00402000 --- OK --- I also tried clean build with dflags -m32mscoff. But then I get another kind of errors. Any help moving forward is appreciated. Hi there, Compiling with 2.085.1 on Windows 10 works with `dub --arch=x86_mscoff` LDC 1.15.0 works for x86/x86_64. Tested also on a fresh VMWare instance running Windows 7. You can try running it with `dub --arch=x86_mscoff --verbose` in order to get more diagnostic messages for build errors. Make sure you have "Visual C++ Redistributable for Visual Studio 2015" installed, it is required to be able to run the produced executable, if you don't build it using the Visual Studio command line. The reason is that both DMD and LDC will use the MinGW `.lib` files, which require a dynamic linked C runtime (static linking is permitted only with Visual Studio)
Re: Overloads not returning appropriate info. [Field reflunkory]
On Monday, 8 April 2019 at 12:26:28 UTC, Adam D. Ruppe wrote: On Sunday, 7 April 2019 at 17:42:58 UTC, Alex wrote: That is blatantly wrong. The code works EXACTLY the same way with and without using stringof. In some cases, yeah. In the general case, no. Your import hack* is only there because of stringof. Using the local symbol, there is no need to import the module. This means you avoid name conflicts with local symbols (like I pointed out in the linked post) and it has the potential to avoid protection violation errors, since you are no longer getting the symbol from your module; it is gotten somewhere else, ideally from its own module, and passed to you, which is allowed even for private or hidden symbols. It also just makes the code a lot simpler, so there's no more need to jump through hoops to debug it. But I've already said the point of using T.stringof is so that one gets what T is and that actually helps debugging. You don't think I didn't try using T first? Why would I type extra symbols if it work exactly fine the first time? The reason I added `~T.stringof~` which is 11 more chars than T.` was precisely because the code wasn't working and I was trying to figure out why. to claim that it's absolutely wrong in all cases is ignorant. I realize that in many cases it is unnecessary and in some cases it will break the code(requiring an import because one is not using the type but the id which is then hidden)... But as I said, I did a search and replace that it didn't change squat as far as the code. The main issue was using that typeof which you didn't catch cause you were too busy trying to make an issue out of stringof. The other issues either remain, even after using your "rule", or I had to refactor the code and use different traits(such as the one you recommended for fields). My point is that you are going ape shit over using T.stringof, you posted no real reasons why it is absolutely unnecessary yet claimed was after I already shown that it has some use. It's one thing to make a suggestion and say "You know, you don't have to use T.stringof since it will function better in general, try it without it and see if fixes your problems" rather than keep on beating a dead horse. * https://github.com/IncipientDesigns/Dlang_Reflect/blob/master/mReflect.d#L61 I have removed all T.stringof's in the code and I still get the exact same errors. That's the first step. Then, you clean up the hacks that were introduced to work around stringof's problems and get a better design that actually works, like passing private members from one module to another via alias parameters. I don't know what you are talking bout passing private members from one module using alias parameters. There is only one module that does the reflection and all the "passing" of private parameters are done INSIDE that module. If you mean that I should pass the initial class as an alias, well, I tried that initially and it worked for some things but failed for others so went back and forth between using alias and types. The problem is because there are issues in D's type system and when they create hard to track bug one has to screw with shit to figure out what is going on and that introduces dead ends which may or may not be modify the design incipiently... which is the whole damn reason I'm writing the reflection library in the first place... to avoid all these issues with traits and provide a common interface... I mean, half the shit in __traits looks like it could be in std.traits and there is no clear reason why there are two aspects of D that do essentially the same thing. Also there are many "holes" in traits that require compound solutions(such as filter members to specific types) which then creates ugly CT code(multiple nested loops). one could just open the source if there was anything to "hide" That's not necessarily true, it is possible to have code exclude private members. In fact, it is often considered good practice to do that for library releases for encapsulation! I'm not sure what you are talking about here. I assume you mean the body, which I'm not talking about. The body is irrelevant. You can't even get the body using __traits. I'm talking about if the symbol exists, private or not, one can see it in the source code since, for it to be marked private it must show up in the source. So, "private" does actually hide shit in the source code. It may hide the functionality/body/binary code, but marking a member private doesn't HIDE anything in the source. Protection is a runtime thing(except for CTFE). Protection *only* exists at compile time - at runtime, there's zero checks. There's nothing preventing you from passing a pointer to a private member, for example. No, you really are missing the point. Protection is a RUNTIME thing. Else one would just make all members public. Protection exists at compile
Re: What Does @ Mean?
On Monday, 8 April 2019 at 14:27:11 UTC, JN wrote: Java uses @ for annotations too. Pascal uses @ for "address of", like & in D. Just one of the many reasons I balked at Java... many MANY reasons. Thanks, JN.
Re: What Does @ Mean?
On Monday, 8 April 2019 at 14:19:04 UTC, XavierAP wrote: On Monday, 8 April 2019 at 11:58:49 UTC, Ron Tarrant wrote: And while I'm asking, does an underscore have special meaning when used either at the beginning or end of a variable name? In D, @ is used as Adam has explained as a prefix indicating attributes (either user-defined ones or, confusingly enough, some of the standard ones). Yup. Confusion. Yup. :) Of course you should never do this unless you absolutely need for interop. No fear of that. I was just trying to understand the example I cited. For example in D you could have a public property length and a private member _length. This seems like a good practice. In this case I've seen some other annoying conventions, for example private member variables being prefixed with m_ The things I missed by not getting my degree... or by not keeping my nose to the grindstone for the last 30-odd years. :) Thanks, Xavier.
Re: What Does @ Mean?
On Monday, 8 April 2019 at 14:19:04 UTC, XavierAP wrote: The only other example of language using @, in an almost but not quite completely different way, is C#. It's also a prefix that allows you to define names that would collide with reserved words, for example string @class = "menu"; Of course you should never do this unless you absolutely need for interop. Java uses @ for annotations too. Pascal uses @ for "address of", like & in D.
Re: What Does @ Mean?
On Monday, 8 April 2019 at 11:58:49 UTC, Ron Tarrant wrote: And while I'm asking, does an underscore have special meaning when used either at the beginning or end of a variable name? In D, @ is used as Adam has explained as a prefix indicating attributes (either user-defined ones or, confusingly enough, some of the standard ones). The only other example of language using @, in an almost but not quite completely different way, is C#. It's also a prefix that allows you to define names that would collide with reserved words, for example string @class = "menu"; Of course you should never do this unless you absolutely need for interop. Underscore prefixes are used in some languages by pure user convention mainly for private members (fields), to avoid name clashing. For example in D you could have a public property length and a private member _length. Python takes this a step further. Since it supports classes but no public/private visibility at all, users and IDEs have convened to use (one or two) underscore prefixes to signal members that aren't meant to be accessed publicly from outside the class, even if there's nothing stopping you (besides auto code completion not showing them). For C and C++ the convention (recognized by the standards) is different: names prefixed by any number of underscores are all reserved; basically because the global namespace is so badly polluted already. In this case I've seen some other annoying conventions, for example private member variables being prefixed with m_
Re: Iterate/sort associative array by value?
Le 07/04/2019 à 19:16, Seb via Digitalmars-d-learn a écrit :
Then you can do:
---
["a": 1].byPair.array.sort!((a, b) => a.value < a.value).release.each!writeln;
---
You'll have a sorted array with key and value props.
That's what I would do: just operating on an array of {k,v} pairs.
--
diniz {la vita e estranj}
Cannot link vibe.d sample / optlink error
I used dmd 2.085.0 and 2.085.1 on Win 10 I followed sample at https://vibed.org/blog/posts/a-scalable-chat-room-service-in-d Just the beginning, where you you should compile hello word web app. command line: "dub" compilation finishes ok. then it prints "Linking..." and I get window message box: --- Unexpected OPTLINK Termination at EIP=0040F60A --- EAX=073D EBX=00438C70 ECX=0B2F EDX=038A ESI=008F EDI=073D1344 EBP=0019FF28 ESP=0019FEE0 First=00402000 --- OK --- I also tried clean build with dflags -m32mscoff. But then I get another kind of errors. Any help moving forward is appreciated.
Re: Templates - What's Up with the template keyword?
On Monday, 8 April 2019 at 12:40:10 UTC, Adam D. Ruppe wrote: You don't need template keyword for the majority of cases because the compiler lets you do shortcuts. Thanks, Adam. Good to know. (maybe I am looking at the wrong part of the book, it is hard to find the right section/page number online). My bad. The edition I'm working from was released 2018-10-17 and can be found here: http://ddili.org/ders/d.en/Programming_in_D.pdf The page number in online PDF viewer is 421 and the example is about 1/3 of the way down the page.
Re: What Does @ Mean?
Well, that was quick! Thanks Adam, Kagamin, and Alex.
Re: Templates - What's Up with the template keyword?
On Monday, 8 April 2019 at 12:23:28 UTC, Ron Tarrant wrote:
But in "Programming in D," (self, 2009-2018) by Ali Çehreli,
there's no mention of the 'template' keyword in any of his
examples.
You don't need template keyword for the majority of cases because
the compiler lets you do shortcuts.
If you write
void foo(T)(int a) {}
the compiler sees that as a shortcut of writing
template foo(T) {
void foo(int a) {}
}
and does all the necessary expansion for you.
Writing long-form templates is for when you need to do it more
advanced topics. Like a template is allowed to have several
members if you write it long-form. You can also use it to force a
specific strategy like CTFE inside the template (though the
compiler now has shortcuts for that too, so you don't see it
written long-form much more in new code).
Point!T getResponse(T : Point!T)(string question)
This looks wrong...
getResponse(T : Point)
should work (and is what I see in the book), but `T : Point!T` is
different.
So what the colon does is specialize the template - it says "if
you pass a type matching `Point` (the stuff after the colon), use
this function instead of the generic function".
The reason `T : Point!T` isn't compiling is that that's saying
only match a recursive template... and you don't have one of
those.
You probably are thinking something along the lines of
Point!T getResponse(T : Point!R, R)(string question) {}
(maybe I am looking at the wrong part of the book, it is hard to
find the right section/page number online). This is one of the
most advanced template forms which is able to deconstruct other
templates.
So, if you call that with a
Point!int p;
getResponse!(typeof(p))("my question")
then it will match T as being some kind of `Point!R`... and it
will take apart the R into its own argument.
So when given Point!int, it will see the part after ! happens to
be int, and make R == int.
Thus, inside the getResponse function:
T == Point!int
R == int
and you can inspect that and react accordingly. Or you can ignore
the R and just use the Point. The value here is you could pass
Point!int or Point!float or Point!whatever all to the one
function.
(You can also do this if you just use an unrestricted T argument,
but the Point!R specialization will make the intent more clear in
documentation and lets you take it apart if you need to know what
R is.)
Re: Overloads not returning appropriate info. [Field reflunkory]
On Sunday, 7 April 2019 at 17:42:58 UTC, Alex wrote: That is blatantly wrong. The code works EXACTLY the same way with and without using stringof. In some cases, yeah. In the general case, no. Your import hack* is only there because of stringof. Using the local symbol, there is no need to import the module. This means you avoid name conflicts with local symbols (like I pointed out in the linked post) and it has the potential to avoid protection violation errors, since you are no longer getting the symbol from your module; it is gotten somewhere else, ideally from its own module, and passed to you, which is allowed even for private or hidden symbols. It also just makes the code a lot simpler, so there's no more need to jump through hoops to debug it. * https://github.com/IncipientDesigns/Dlang_Reflect/blob/master/mReflect.d#L61 I have removed all T.stringof's in the code and I still get the exact same errors. That's the first step. Then, you clean up the hacks that were introduced to work around stringof's problems and get a better design that actually works, like passing private members from one module to another via alias parameters. one could just open the source if there was anything to "hide" That's not necessarily true, it is possible to have code exclude private members. In fact, it is often considered good practice to do that for library releases for encapsulation! Protection is a runtime thing(except for CTFE). Protection *only* exists at compile time - at runtime, there's zero checks. There's nothing preventing you from passing a pointer to a private member, for example. This is why __traits(getMember) fails the same as T.name, but it is also the reason why there's hope to cheat here, at least once you get a correct foundation laid, by using mixin templates and/or passing aliases cross module. (interestingly, .tupleof does let you bypass privacy protections, but only for aggregate members, not for methods.)
Templates - What's Up with the template keyword?
I'm digging into templates in an attempt to understand the
signals-n-slots replacement for the observer pattern, but I've
got a question I can't seem to find an answer for and an example
for which I'm unable to solve the error.
First, the question...
In Michael Parker's book, "Learning D," (Packt, 2015) on page 160
he gives an example of a basic template:
template MyTemplate(T)
{
T val;
void printVal()
{
import std.stdio : writeln;
writeln("The type is ", typeid(T));
writeln("The value is ", val);
}
}
But in "Programming in D," (self, 2009-2018) by Ali Çehreli,
there's no mention of the 'template' keyword in any of his
examples.
Has the 'template' keyword been deprecated? Or is it optional?
And now, my broken code...
In Ali's book (section 64.7, page 401) this example is given:
Point!T getResponse(T : Point!T)(string question)
{
writefln("%s (Point!%s)", question, T.stringof);
auto x = getResponse!T(" x");
auto y = getResponse!T(" y");
return Point!T(x, y);
}
But I'm having trouble working out how this would be used. Up to
this point, either the usage case is given or I was able to work
it out on my own, but this one seems to demand a use case outside
the scope of what's been covered in the chapter so far and I'm
lost.
My full code for this example:
-
import std.stdio;
import std.math;
import std.string;
struct Point(T)
{
T x;
T y;
T distanceTo(Point that) const
{
immutable real xDistance = x - that.x;
immutable real yDistance = y - that.y;
immutable distance = sqrt((xDistance * xDistance) + (yDistance
* yDistance));
return(cast(T)distance);
} // distanceTo()
} // struct Point
Point!T getResponse(T : Point!T)(string question)
{
writefln("%s (Point!%s)", question, T.stringof);
auto x = getResponse!T(" x");
auto y = getResponse!T(" y");
return(Point!T(x, y));
} // getResponse() Point!T
void main()
{
auto wayPoint1 = getResponse!Point("Where is the first map
location?");
auto wayPoint2 = getResponse!Point("Where is the second map
location?");
writeln("Distance: ", wayPoint1.distanceTo(wayPoint2));
} // main()
--
(lines 47 & 48) Error: template instance `getResponse!(Point)`
does not match template declaration getResponse(T :
Point!T)(string question)
Any help will be very much appreciated.
Re: What Does @ Mean?
On Monday, 8 April 2019 at 11:58:49 UTC, Ron Tarrant wrote:
Would someone please tell me what an at sign (@) means when
it's used like this:
bool isLeaf() @property
In that case, it means nothing. We just defined the word to be
`@property`, with the @ included. So it is just part of the name.
Same with @safe, @trusted, @system, @nogc, and a few others built
into the language.
It was arbitrary decided to put the @ in the words so it wouldn't
conflict with existing variable names like `int safe;`
In some other contexts though, it just indicates to the parser
that it is a user-defined attribute instead of continuing the
declaration with a name. In these, it is a prefix to another user
value. For example:
struct MyCustomAttribute {} // perfectly ordinary struct
@MyCustomAttribute() void func() {}
In that function, the @ before the name MyCustomAttribute tells
the compiler that it is just an annotation instead of a return
value or the defined name of the new function.
So, two purposes for the @: it is just part of some built-in
keywords, and it can indicate you are using a user-define d name
as an attribute/annotation instead of as a return value, etc.
And while I'm asking, does an underscore have special meaning
when used either at the beginning or end of a variable name?
Nothing special there, you are allowed to use the _ anywhere in a
name. Some people use it as a convention on private members,
unused members, or keyword conflicts (like `body_` so the
compiler doesn't see it as the keyword `body`).
But it is just a user convention, it doesn't mean anything
special to the compiler... except:
How about a double underscore?
A leading double underscore is somewhat special. Those are
allowed in any name, but those are reserved for compiler
implementation details.
So like `__ctor` is the special name the compiler uses for
constructors. You can call it (though since this is an internal
compiler implementation detail you are choosing to exploit, it is
liable to break at any time) or define stuff with these names to
do various hacks.
You should avoid __names though since the compiler reserves them
for its own use.
Re: Pass template parameter into q{} string
Maybe just use mixin template?
mixin template f(alias values)
{
static foreach(v;values)
mixin("bool " ~ v ~ " = false;");
}
int main()
{
enum string[] a=["a","b"];
mixin f!a;
return 0;
}
Re: What Does @ Mean?
https://dlang.org/spec/function.html#property-functions
Re: What Does @ Mean?
On Monday, 8 April 2019 at 11:58:49 UTC, Ron Tarrant wrote:
This is frustrating and makes me feel like a complete newb.
Worse, it's impossible to search for. Ever try Googling a
single character?
The D documentation also doesn't seem to explain the meaning of
this or any other token. Sure, most of them are obvious, but
this one eludes me. All I can find is this:
https://dlang.org/spec/lex.html#tokens
Would someone please tell me what an at sign (@) means when
it's used like this:
bool isLeaf() @property
{
return children.length == 0;
}
In fact, I have no idea what @ means anywhere other than in an
email address. Is this a common thing in contemporary languages?
And while I'm asking, does an underscore have special meaning
when used either at the beginning or end of a variable name?
How about a double underscore?
I know underscores are sort of left over from C, but do these
characters have special meaning in D or are they simply a
convention... like T in a template definition?
Some of the attributes in D go with an "@".
https://forum.dlang.org/post/fiwfcsqmjsndcjixi...@forum.dlang.org
https://wiki.dlang.org/Language_Designs_Explained
https://dlang.org/spec/attribute.html
Re: D threading and shared variables
On Sunday, 7 April 2019 at 14:49:20 UTC, Archie Allison wrote: The codebase is a reasonable size so too big (and proprietary) to share. You can reduce it to a minimal example that doesn't work. Static variables are thread local by default in D unless they are marked as shared or __gshared.
What Does @ Mean?
This is frustrating and makes me feel like a complete newb.
Worse, it's impossible to search for. Ever try Googling a single
character?
The D documentation also doesn't seem to explain the meaning of
this or any other token. Sure, most of them are obvious, but this
one eludes me. All I can find is this:
https://dlang.org/spec/lex.html#tokens
Would someone please tell me what an at sign (@) means when it's
used like this:
bool isLeaf() @property
{
return children.length == 0;
}
In fact, I have no idea what @ means anywhere other than in an
email address. Is this a common thing in contemporary languages?
And while I'm asking, does an underscore have special meaning
when used either at the beginning or end of a variable name?
How about a double underscore?
I know underscores are sort of left over from C, but do these
characters have special meaning in D or are they simply a
convention... like T in a template definition?
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 07:53:23 UTC, Robert M. Münch wrote: Why does DMD not give a hint, that an import from the standard lib might be missing? I find these explicit import statements very annyoing. There currently are a few hard-coded import hints for common functions: https://github.com/dlang/dmd/blob/master/src/dmd/imphint.d But it definitely could be better. As Sebastian said, you can do `import std.experimental.all;` or from version 2.086 `import std;` to import the entire standard library. If dmd as a library pans out, a language server might automatically suggest imports for unresolved symbols like common Java and C# IDEs do.
Re: Iterate/sort associative array by value?
On Monday, 8 April 2019 at 07:53:23 UTC, Robert M. Münch wrote:
On 2019-04-07 19:28:02 +, Dennis said:
Did you import it? import std.algorithm;
:-/ of course not...
Why does DMD not give a hint, that an import from the standard
lib might be missing?
It does do this, so the question should be: why aren't its
warnings
more extensive?
Example:
void main() {
writeln("Hello, world!");
}
Fails to compile with this error:
./missing.d(4): Error: writeln is not defined, perhaps import
std.stdio; is needed?
That seems to come from src/dmd/expressionsem.d , which uses
importHint from
src/dmd/imphint.d , which just has this list:
shared static this()
{
// in alphabetic order
hints = [
"calloc": "core.stdc.stdlib",
"cos": "std.math",
"fabs": "std.math",
"free": "core.stdc.stdlib",
"malloc": "core.stdc.stdlib",
"printf": "core.stdc.stdio",
"realloc": "core.stdc.stdlib",
"sin": "std.math",
"sqrt": "std.math",
"writefln": "std.stdio",
"writeln": "std.stdio",
"__va_argsave_t": "core.stdc.stdarg",
"__va_list_tag": "core.stdc.stdarg",
];
}
Re: Iterate/sort associative array by value?
On 2019-04-07 19:28:02 +, Dennis said: Did you import it? import std.algorithm; :-/ of course not... Why does DMD not give a hint, that an import from the standard lib might be missing? I find these explicit import statements very annyoing. DMD should build up a database of stuff it knows about (provided via a config file where to find what) and auto-import just the things I use/need. The current system is legacy based like it is in C since 40 years... Anyway, might be worth a topic on its own... -- Robert M. Münch http://www.saphirion.com smarter | better | faster
