On Saturday, 13 May 2017 at 18:32:16 UTC, Lewis wrote:
import std.random;
import std.stdio;
int[4] testfunc(int num) @nogc
{
return [0, 1, num, 3];
}
int main()
{
int[4] arr = testfunc(uniform(0, 15));
writeln(arr);
return 0;
}
I've read a bunch of stuff that seems to indicate that array
literals are always heap-allocated, even when being used to
populate a static array.
On the contrary, when initializing static arrays, allocation is
not needed.
Note that what's *conceptually* happening in testfunc is this:
int[4] testfunc(int num) @nogc
{
typeof(return) result = [0, 1, num, 3];
return result;
}
i.e. the type and size of the storage is known beforehand, all
there is to do is copy the elements:
000000000044e528 <@nogc int[4] test.testfunc(int)>:
44e528: 55 push %rbp
44e529: 48 8b ec mov %rsp,%rbp
44e52c: 48 83 ec 10 sub $0x10,%rsp
44e530: 48 89 7d f8 mov %rdi,-0x8(%rbp)
44e534: c7 07 00 00 00 00 movl $0x0,(%rdi) #
0 goes at offset 0
44e53a: c7 47 04 01 00 00 00 movl $0x1,0x4(%rdi) #
1 at offset 4
44e541: 89 77 08 mov %esi,0x8(%rdi) #
parameter at offset 8
44e544: c7 47 0c 03 00 00 00 movl $0x3,0xc(%rdi) #
3 at offset 12
44e54b: 48 8b 45 f8 mov -0x8(%rbp),%rax
44e54f: c9 leaveq
44e550: c3 retq
Is all the old stuff I was reading just out-of-date now?
Where exactly did you read that initialization of a static array
requires an allocation? That source should be abolished...
errrm... corrected!
