Re: Hipreme's #1 Tip of the day
On Wednesday, 19 October 2022 at 23:28:46 UTC, Hipreme wrote:
Hey guys, I'm going to start making a tip of the day (although
I'm pretty sure I won't be able to give every day a tip), but
those things are really interesting to newcomers to know and
may be obvious to some of the old schoolers there.
Always public import a type that the user (including you) is
expected to interact with:
Imagine we have a module A that define a tree
```d
module a;
struct Tree(T){}
```
If you create a module b containing a function that returns a
tree:
```d
module b;
import a;
Tree!string getDirectoryTree(string entry){return null;}
```
This is virtually unusable! One must `public import a: Tree;`
This will make your API a lot easier to interact with, keep in
mind to always public import some type that is used from
another dependency like this, but try to not overdo it.
Will add an important tip for when handling variables of integer
type smaller than `int` :
```D
ushort a, b, c;
c = a + b;//expression a + b will be promoted to int or compiler
will emit a deprecation warning
c = cast(ushort) (a + b);//works fine
c = cast(typeof(c)) (a + b);//alternate form
c = cast(ushort) a + b;//bad, only "a" will be casted so you get
promoted to int/warned anyway
c += a;//assigning operators' operands won't be promoted, with
same types at least
auto d = a + b;//will probably be of type int
```
note: i didn't 101% check but the above holds true in my usage at
least.
Hipreme's #1 Tip of the day
Hey guys, I'm going to start making a tip of the day (although
I'm pretty sure I won't be able to give every day a tip), but
those things are really interesting to newcomers to know and may
be obvious to some of the old schoolers there.
Always public import a type that the user (including you) is
expected to interact with:
Imagine we have a module A that define a tree
```d
module a;
struct Tree(T){}
```
If you create a module b containing a function that returns a
tree:
```d
module b;
import a;
Tree!string getDirectoryTree(string entry){return null;}
```
This is virtually unusable! One must `public import a: Tree;`
This will make your API a lot easier to interact with, keep in
mind to always public import some type that is used from another
dependency like this, but try to not overdo it.
Re: Find out what type my class is being converted to for comparisons
On Tuesday, 18 October 2022 at 18:53:41 UTC, Matthew Rushworth
wrote:
I am in the process of building a matrix class (uni project,
with my choice of programming language) and appear to have run
into a problem that I'm not too sure how to fix.
My class uses templates to define the shape of the matrix,
although I'm not sure if that matters. As part of my class, I
included a opEquals, but when I try to assert that a matrix
created by multiplying with the identity matrix matches the
output (I checked with liberal writeln()s to make sure they do)
but my opEquals() function (I moved it out of the class as I
kept getting errors saying it was supposed to be non-const, and
couldn't figure out how to fix that either) just isn't called.
---
Matrix code (the only bit of the class used by opEquals):
```
class Matrix(size_t X, size_t Y = X){
const size_t x_length = X;
const size_t y_length = Y;
double[X*Y] data;
...
}
```
The entirety of opEquals:
```
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X,Y) m1, const
Matrix!(X,Y) m2) {
for (int i = 0; i < m1.data.length; ++i) if (m1.data[i] !=
m2.data[i]) return false;
return true;
}
```
and the code that excepts:
```
void main() {
auto m = new Matrix!(2)();
m.data = [1.0,0.0,0.0,1.0].dup;
auto n = new Matrix!(2)();
n.data = [2.0,3.0,4.0,5.0].dup;
auto u = mult(m,n);
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
// using opEquals() directly is working, but it doesn't
seem to be being used
//assert(opEquals(u,n),"\"opEquals(u, n)\" is
failing."); // this works fine
assert(u == n,"\"u == n\" is failing."); // this fails.
Why?
}
```
---
Any help would be very much appreciated. A way to figure out
what the '==' is converting its arguments to would also be
great, but I'm not sure it exists (beyond just sitting down and
trying to work it out myself, of course)
What's the reason for it being a class? struct makes more sense
here, plus it'll be faster
If it were a struct, you'd not need any of that, and you can also
have operator overloading for your mult while also being able to
check how many row/col at compile time, here an example:
```D
import std;
struct Matrix(size_t X, size_t Y = X)
{
enum x_length = X; // enum so it's available only at compile
time
enum y_length = Y;
double[X * Y] data;
// operator overloading
Matrix opBinary(string op)(Matrix rhs)
{
static if (op == "*")
{
//
// ** ADD YOUR MULT OPERATION HERE **
//
static if (X == 2)
{
return Matrix();
}
else
static assert("not supported");
}
else
static assert(0, "Operator " ~ op ~ " not
implemented");
}
}
void main()
{
// check equality by value:
auto a = Matrix!(2)();
a.data = 0;
auto b = Matrix!(2)();
b.data = 0;
writeln("are they the same?: ", a == b); // it'll check for
equality by value
auto m = Matrix!(2)();
m.data = [1.0, 0.0, 0.0, 1.0];
auto n = Matrix!(2)();
n.data = [2.0, 3.0, 4.0, 5.0];
// here we can use the * operator!
auto u = m * n;
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
}
```
Re: Catching C errors
On Wednesday, 19 October 2022 at 16:47:49 UTC, data pulverizer wrote: On Wednesday, 19 October 2022 at 14:05:35 UTC, data pulverizer wrote: Hi all, I am calling code from a C API, and would like to know how to catch exit errors so that they can be handled and make them more like an exceptions so that the computation can continue. I've tried something similar to what is outlined here: https://dlang.org/phobos/object.html#.Error but it doesn't work, the process dies in the try block. Thanks It's okay, I've found a work around. Always good to share what it is, for future readers who have the same question
Compiler Error while using Validation in the hunt-framework
Hello,
I started playing with D and the hunt-framework. But I bumped
into an error using Validation.
```d
module app.forms.LoginForm;
import hunt.validation;
import hunt.framework.http.Form;
class LoginForm : Form {
mixin MakeForm;
@Email
string name;
@Length(3,8)
string password;
}
```
The error looks like that:
`../hunt/validation/DeclDef.d-mixin-41(54,108): Error: undefined
identifier arg`
When I remove the parameters from `@Length`, it compiles.
I tried the `dicoth` example application, but I get the same
error for the validation used there.
I use this compiler: DMD64 D Compiler v2.100.2
under Linux.
My current D knowledge is not sufficient to fix the bug. No idea
how the annotation and mixin templates work together here. I
didn't find any documentation, how to write custom annotations.
Can somebody give me a hint?
BR Roman
Re: Catching C errors
On 10/19/22 09:47, data pulverizer wrote: > It's okay, I've found a work around. Do you simply check the return value? Ali
Re: Catching C errors
On 10/19/22 07:05, data pulverizer wrote: > I am calling code from a C API, and would like to know how to catch exit > errors If you are talking about the exit() Posix function, you can't do anything about that because its purpose is to cause "normal process termination". Ali
Re: Catching C errors
On Wednesday, 19 October 2022 at 14:05:35 UTC, data pulverizer wrote: Hi all, I am calling code from a C API, and would like to know how to catch exit errors so that they can be handled and make them more like an exceptions so that the computation can continue. I've tried something similar to what is outlined here: https://dlang.org/phobos/object.html#.Error but it doesn't work, the process dies in the try block. Thanks It's okay, I've found a work around.
Catching C errors
Hi all, I am calling code from a C API, and would like to know how to catch exit errors so that they can be handled and make them more like an exceptions so that the computation can continue. I've tried something similar to what is outlined here: https://dlang.org/phobos/object.html#.Error but it doesn't work, the process dies in the try block. Thanks
Re: Find out what type my class is being converted to for comparisons
On 10/19/22 00:43, Matthew Rushworth via Digitalmars-d-learn wrote: Thank you, that worked perfectly, not sure exactly what I did wrong, I'm assuming I forgot to make the parameter a const variable Object, the root of the class object hierarchy already defines an opEquals [1] and you need to overload/overwrite that for it to work properly. Only class methods are considered, hence ag0aep6g's suggestion. [1] https://dlang.org/library/object/object.op_equals.html
Re: Can someone tell me what the compiler thought I was trying to do?
On Wednesday, 19 October 2022 at 05:41:26 UTC, zjh wrote: Why always afraid to `add features`? C++ is `so complicated` ,but that people are not afraid to continue to `add features`. Look at the `emerging` languages, which are not crazy about `adding features`. Even `go` is adding generics.
Re: Can someone tell me what the compiler thought I was trying to do?
On Wednesday, 19 October 2022 at 05:50:18 UTC, zjh wrote: In my opinion, as long as `users` have reasonable needs, languages should added corresponding features, instead of becoming religions. `Some features` are very popular for users,I really don't know why they didn't add it. When you show `prejudice`, users are lost. Like `class`, when it can be used as the smallest `encapsulation unit`, it can provide `this feature` but intentionally does not. Just like when you ride a bicycle, but it has a `square` tire.
