Re: Creating 1000 instances
On Friday, 19 February 2021 at 10:02:05 UTC, Siemargl wrote:
On Friday, 19 February 2021 at 08:29:36 UTC, Ferhat Kurtulmuş
wrote:
Since classes are reference types all instances of files will
be the same reference of "new File()", which you probably
don't want.
Is any differences between x and y definitions?
MyClass [] x, y;
x = new MyClass[7];
y= new MyClass[](8);
The only part of the documentation I've found that talks about
this is here:
https://dlang.org/spec/expression.html#new_expressions
The main difference I know of comes with multidimensional arrays:
auto a = new int[4][4];
pragma(msg, typeof(a)); // Prints int[4][]
auto b = new int[][](4,4);
pragma(msg, typeof(b)); // Prints int[][]
Since the former is a dynamic array of static arrays, the first
size parameter cannot be passed at runtime:
auto n = 4;
// Error: variable n cannot be read at compile time
auto c = new int[n][n];
But must be a compiletime constant:
enum N = 4;
auto d = new int[N][n];
pragma(msg, typeof(d)); // Prints int[4][]
The other syntax however, can take runtime values, but does not
encode the size in the type:
auto e = new int[][](n,n);
pragma(msg, typeof(e)); // Prints int[][]
The other big thing about the []() syntax is it actually
initializes the arrays of arrays for you:
assert(e[0].length == n);
If you were to use new int[][n], you would need to initialize
each array of arrays manually:
auto f = new int[][n];
assert(f[0].length == 0); // it's empty
foreach (i; 0..n) {
f[i] = new int[n]; // Have to do this yourself.
}
--
Simen
Re: Creating 1000 instances
On Friday, 19 February 2021 at 10:02:05 UTC, Siemargl wrote: On Friday, 19 February 2021 at 08:29:36 UTC, Ferhat Kurtulmuş wrote: Since classes are reference types all instances of files will be the same reference of "new File()", which you probably don't want. Is any differences between x and y definitions? MyClass [] x, y; x = new MyClass[7]; y= new MyClass[](8); Although I don't usually use the latter, I can say online d editor yields the same ASM output for both: File[] files = new File[10]; File[] files = new File[](10);
Re: Creating 1000 instances
On Friday, 19 February 2021 at 08:29:36 UTC, Ferhat Kurtulmuş wrote: Since classes are reference types all instances of files will be the same reference of "new File()", which you probably don't want. Is any differences between x and y definitions? MyClass [] x, y; x = new MyClass[7]; y= new MyClass[](8);
Re: Creating 1000 instances
On Friday, 19 February 2021 at 08:29:36 UTC, Ferhat Kurtulmuş wrote: On Friday, 19 February 2021 at 08:04:19 UTC, Виталий Фадеев wrote: [...] files = new File[]( 1000 ); files[] = new File(); // add this Since classes are reference types all instances of files will be the same reference of "new File()", which you probably don't want. You can do files[].each!((ref a) => a = new File);
Re: Creating 1000 instances
On Friday, 19 February 2021 at 08:41:06 UTC, Ferhat Kurtulmuş wrote: On Friday, 19 February 2021 at 08:29:36 UTC, Ferhat Kurtulmuş wrote: On Friday, 19 February 2021 at 08:04:19 UTC, Виталий Фадеев wrote: [...] files = new File[]( 1000 ); files[] = new File(); // add this Since classes are reference types all instances of files will be the same reference of "new File()", which you probably don't want. You can do files[].each!((ref a) => a = new File); oh, now we can remove brackets files.each!((ref a) => a = new File);
Re: Creating 1000 instances
On Friday, 19 February 2021 at 08:04:19 UTC, Виталий Фадеев wrote:
We have:
class File
{
// WIN32_FIND_DATAW data;
}
void fastReadDir()
{
File[] files;
// reserve space, allocating instances
files = new File[]( 1000 ); // <--- trouble here ?
// filling instances
auto file = files.ptr;
writeln( file.data );// <--- or trouble here ?
// ...
}
Got:
SegFault
Goal:
Allocate memory for 1000 instances at once.
Source:
https://run.dlang.io/is/xfaXcv
Question:
What is the true, fastest, beauty way to create 1000
instances of the class File ?
files = new File[]( 1000 );
files[] = new File(); // add this
Since classes are reference types all instances of files will be
the same reference of "new File()", which you probably don't want.
Creating 1000 instances
We have:
class File
{
// WIN32_FIND_DATAW data;
}
void fastReadDir()
{
File[] files;
// reserve space, allocating instances
files = new File[]( 1000 ); // <--- trouble here ?
// filling instances
auto file = files.ptr;
writeln( file.data );// <--- or trouble here ?
// ...
}
Got:
SegFault
Goal:
Allocate memory for 1000 instances at once.
Source:
https://run.dlang.io/is/xfaXcv
Question:
What is the true, fastest, beauty way to create 1000
instances of the class File ?
