change object class
Hi!
I want to change a method ```Draw``` on a custom object when the
```MouseIn``` event occurs.
This is known as "Change State" of the object: ```Init``` ->
```Hovered```.
I want to change the state of an object by changing its class,
like this:
```d
this.__vptr = typeid(CLS).vtbl.ptr;
```
I have read the ABI and am confident in replacing ```__vptr``` as
long as the classes contain the same fields and the same
interfaces.
Example:
```d
// O
// to!state
// State_Init: O
// Draw
// State_Hovered : O
// Draw
//
// o.to!State_Hovered
// o.to!State_Init
class O
{
void to(CLS)()
{
// if (same fields && same interfaces && same instance size)
this.__vptr =
cast(immutable(void*)*)typeid(CLS).vtbl.ptr;
}
}
State_Init : O
void Draw() { /* ... */ }
State_Hovered : O
void Draw() { /* ... */ }
```
when MouseIn:
```d
...
o.to!State_Hovered();
...
```
when MouseOut:
```d
...
o.to!State_Init();
...
```
It works! But I want to ask how to make this 100% the best of the
best?
What should I consider before changing ```__vptr``` ?
dlang custom keyword for struct/class
Is it possible to write like this in D?
```d
struct Message
{
ulong timestamp;
}
Message LongMessage
{
ubyte[255] s;
}
//
// it mean
//
// struct LongMessage
// {
// Message _super;
// alias _super this;
// ubyte[255] s;
// }
//
// or
//
// struct LongMessage
// {
// ulong timestamp;
// ubyte[255] s;
// }
```
Is it possible?
Re: dlang custom keyword for struct/class
On Sunday, 17 September 2023 at 15:55:37 UTC, Vitaliy Fadeev
wrote:
Is it possible to write like this in D?
```d
struct Message
{
ulong timestamp;
}
Message LongMessage
{
ubyte[255] s;
}
//
// it mean
//
// struct LongMessage
// {
// Message _super;
// alias _super this;
// ubyte[255] s;
// }
//
// or
//
// struct LongMessage
// {
// ulong timestamp;
// ubyte[255] s;
// }
```
Is it possible?
No, there's no struct inheritance. But you can just write the
`alias this` version manually.
Re: change object class
On Sunday, 17 September 2023 at 15:05:59 UTC, Vitaliy Fadeev wrote: ... Playground: https://run.dlang.io/is/hjcLCk
Re: change object class
On Sunday, 17 September 2023 at 15:05:59 UTC, Vitaliy Fadeev wrote: It works! But I want to ask how to make this 100% the best of the best? What should I consider before changing ```__vptr``` ? If that works for you with that constraint of having exact memory layout then it should be ok. This however is very uncommon pattern and your library users might reject it so keep that in mind if you are going to make public library. Other than that I would suggest at least to make that cast method to return a shallow copy because messing with "this" ptr can be dangerous (make sure to try it with const objects and optimized release builds before using this everywhere). An even better (at least safer, in theory) option would be to make "View" or handle struct that wraps an object(pointer) and tracks such transformations. Of course to think of it now there is yet another opportunity - why not to look for something like ECS then? Because you seem to already treat your objects purely as data containers, that way you can safely detach data from logic and reduce the scope of your components to keep them focused on one task. That is up to you of course.
Dinamyc arrays
I`ve just started learning d and have a question. What should I write to set dinamyc rectangular array length in both dimentions? For example, I have declareted an array: ``` int[][] matrix;``` and want set it as n*n matrix. Thanks
Re: change object class
On Sunday, 17 September 2023 at 17:10:16 UTC, evilrat wrote: On Sunday, 17 September 2023 at 15:05:59 UTC, Vitaliy Fadeev wrote: It works! But I want to ask how to make this 100% the best of the best? What should I consider before changing ```__vptr``` ? If that works for you with that constraint of having exact memory layout then it should be ok. No, this is Undefined Behavior and will likely cause you trouble in the future (as in: some very hard to debug bugs may appear). Better to store the state in the object and select the behavior using a switch on the state. -Johan
Re: Dinamyc arrays
On Sunday, 17 September 2023 at 17:15:34 UTC, Timofey wrote:
I`ve just started learning d and have a question.
What should I write to set dinamyc rectangular array length in
both dimentions?
For example, I have declareted an array:
``` int[][] matrix;```
and want set it as n*n matrix.
Thanks
There are many ways to do this, but I can quickly show you two:
```d
import std.stdio;
void main()
{
int[][] matrix;
enum n = 6;
// method 1:
//matrix = new int[][](n, n); /*
// method 2:
matrix.length = n;
foreach(ref e; matrix)
e.length = n;//*/
matrix.writeln;
}
```
SDB@79
Re: Help on array pointers
On Friday, 15 September 2023 at 16:55:34 UTC, Vino wrote:
On Friday, 15 September 2023 at 15:27:00 UTC, Vino wrote:
On Friday, 15 September 2023 at 02:25:09 UTC, Joe wrote:
On Thursday, 14 September 2023 at 14:21:09 UTC, Vino wrote:
[...]
A pointer is a type that points to something. It's literally
that simple. Every piece of data and code exist somewhere in
memory. Every piece of memory has an address. The address is
what a pointer contains. Sometimes we want a type that is the
address itself rather than a value/number.
[...]
Hi Joe,
Thank you very much for the explanation can you please correct
me if my understanding is incorrect
```
byte[] z; // Creates an array of bytes. That is, the compiler
will create a pointer to an array of memory and track it's
length and deal with memory allocation and all that.
```
If we use the above method then :
The compiler takes care of initilizing the array and free the
memory after the usage.
And this is the recommended method.
```
We can use a pointer as an array also, this is the "old school
way of creating arrays".
int qlen = 5;
int* q = cast(int*)malloc(int.sizeof*qlen);
```
If we use the above method then :
We need to manual initilize the array.
Ensure that the memory is freed after the usage using
try/final block.
By default the memory allocation for arrays in D is based on
GC (expect for std.array containers) if we want to
reduce/avoid GC then we need to use the old school way of
creating the arrays.
In case of using the old school ways then can you guide me
what is wrong in my earlier code that I am getting the below
error and how do I correct the same.
Error
```
Invalid Name passed: /T
double free or corruption (out)
Error: program killed by signal 6
```
Hi All,
At last was able to resolve the issue, but not sure
whether this is the reight solution.
Code:
```
import std.stdio: writeln;
import std.exception: enforce;
import std.range: empty;
import std.format: format;
auto ref testNames(in string[] names) {
enforce(!empty(names), "Names cannot be Empty or Null");
import core.stdc.stdlib;
import std.algorithm: any, canFind;
string[] _names;
size_t len = 19;
char[] invalid = (cast(char*)malloc(char.sizeof *
len))[0..len];
invalid[0 ..len] = 0; //Array Initlization
try {
version(Posix) {
invalid =
['\'','\"',':',';','*','&','/','[',']','-','+','$','#','<','>','{','}','(',')'];
}
foreach(i; names.dup) {
auto result = i.any!(a => invalid.canFind(a));
if(result) { throw new Exception("Invalid Name
passed: %s".format(i)); }
else {_names = names.dup; return _names; }
}
} catch(Exception e) { writeln(e.msg); }
finally { invalid = null; free(invalid.ptr); } //
added invalid = null resolved the issue
return _names;
}
void main () {
writeln(testNames(["/T"]));
}
From,
Vino
char[] invalid = (cast(char*)malloc(char.sizeof * len))[0..len];
This is not the way to go about it. You are mixing "pointer
arrays" with "arrays".
You are creating a pointer array then turning that in to an
array. There is no need to do that. Basically you are copying
what the compiler already does for you.
When you are using arrays([] language) you don't have to worry
about anything. Just use them as arrays directly and let the
compiler deal with memory management. The entire point of
"managed arrays" is to avoid having to manually deal with memory
which can cause problems if one is not careful.
Of course you have to make sure your array used used correctly
but that should be obvious.
char[] invalid = (cast(char*)malloc(char.sizeof * len))[0..len];
is exactly the same as
char[] invalid. EXCEPT that you've forced it to be initialized
with a length of len and went from D in to C then back to D just
to create an array. You are making it much more complex than it
needs to be. There are good tutorials on D arrays that you should
look over. You will see how easy they are.
You could just do char[] invalid = new char[](len); for the same
effect but is nicer. New understands char, malloc only
understands bytes. You should not use malloc in D unless you
explicitly know you need to use it. Malloc is primitive memory
management.
When you use D's symantics for arrays it is much easier... which
is the entire point. You don't even need to free the arrays. D
knows they are local variable sand will free them when out of
scope. It will grow them when they need to grow, etc.
invalid = null; free(invalid.ptr);
That does nothing. you set invalid.ptr to null and are freeing
null so you are not freeing the array.
You don't have to though, the array will be free out of scope(not
in final though so exceptions could cause memory leak) because it
is a D array.
Do not
Re: Dinamyc arrays
On Sunday, 17 September 2023 at 17:15:34 UTC, Timofey wrote:
I`ve just started learning d and have a question.
What should I write to set dinamyc rectangular array length in
both dimentions?
For example, I have declareted an array:
```d
int[][] matrix;
```
and want set it as n*n matrix.
Thanks
You can flatten the mat and use operator overloads. Here's a some
basic code to get started:
```d
struct SquaredMat(T)
{
size_t dim;
T[] array;
this(usize dim)
{
this.dim = dim;
array.length = dim * dim;
}
auto opIndex(size_t x, size_t y)
{
return array[x * dim + y];
}
auto opIndexAssign(size_t x, size_t y, T value)
{
array[x * dim + y] = value;
return this;
}
}
```
Those kind of type should already exist in 3rd part native D
libraries, e.g "MIR" has something called "NDSlice" IIRC.
Re: Help on array pointers
On Sunday, 17 September 2023 at 18:28:36 UTC, Joe wrote: On Friday, 15 September 2023 at 16:55:34 UTC, Vino wrote: [...] [...] char[] invalid = (cast(char*)malloc(char.sizeof * len))[0..len]; This is not the way to go about it. You are mixing "pointer arrays" with "arrays". [...] Thank you very much, I am still newbie for programming and currently concentrating on Arrays/Struct/Pointers/Memory management.
