(apologies for cross-posting here, I feel this is a better place
to ask than in my original post where I only received 1 answer
that seemed in favor of this:
http://d.puremagic.com/issues/show_bug.cgi?id=8008 which was 2
months ago).
Please see to the original post above to see the proposal for the
new syntax for static array litterals
(but please reply here).
Running some simple tests show that this is not just cosmetics
and ease of use but would also lead to significantly reduced
overhead when dealing with static array litterals vs raw C array
litterals, as currently D static array litterals perform costly
heap allocation as intermediate step (as shown in the resulting
assembly).
Here's 2 identical programs in C and D, which, compiled with all
optimization flags, result in 20x speedup for the C version (D
takes 17 sec with dmd -O -release -inline -noboundscheck main).
-----
//main.d
import std.stdio,std.conv;
void main(){
size_t n=100000000,z=0;i=0,j=0;
for(i=0;i<n;i++){
size_t[10] a=[i,i+1,i+2,i+3,i+4,i+5,i+6,i+7,i+8,i+9];
for(j=0;j<9;j++){z+=a[j];}
}
writeln(z);
}
-----
//main.c
#include <stdio.h>
int main(){
size_t n=100000000,z=0;i=0,j=0;
for(i=0;i<n;i++){
size_t a[10]={i,i+1,i+2,i+3,i+4,i+5,i+6,i+7,i+8,i+9};
for(j=0;j<9;j++){z+=a[j];}
}
printf("%lu\n",z);
return 0;
}
-----
Note, the same D program modified as follows runs about as fast
as the C program:
size_t[10] a=void; a[0]=i; a[1]=i+1;
a[2]=i+2;a[3]=i+3;a[4]=i+4;a[5]=i+5;a[6]=i+6;a[7]=i+7;a[8]=i+8;a[9]=i+9;
Having the new syntax auto
a=[i,i+1,i+2,i+3,i+4,i+5,i+6,i+7,i+8,i+9]S would prevent the
intermediate heap allocation and should be at least as fast as
the C version, possibly faster if SSE instructions are used.
Finally, someone suggested somewhere else
(http://www.digitalmars.com/d/archives/digitalmars/D/bugs/Issue_8008_New_static_array_literal_syntax_request_auto_x_1_2_3_S_39709.html)
that this could be done in library code:
auto a = [1, 2, 3].toStatic;
however I don't see how that could be achieved, as by the time
the array reaches the toStatic function, it is a dynamic array
whose length is not known at compile time.
Also, his suggested syntax auto[$] a=[1,2,3] is not as good in my
opinion as it prevents one from directly passing an (anonymous)
static array to a function, eg my_fun([1,2,3]S) vs: auto[$]
a=[1,2,3]; my_fun(a);
Thanks for your comments!
