On Tue, 26 Mar 2013 23:21:35 -0400, deadalnix <deadal...@gmail.com> wrote:
On Tuesday, 26 March 2013 at 23:57:32 UTC, bearophile wrote:
Timon Gehr:
IOW, what is the point of "null" if you can just use [].
I usually prefer to use [], because null is a literal for pointers and
class references, while [] is a literal specific for arrays (and
strings), so its meaning is more clear (in D I'd even like a [:]
literal that represents an empty associative array).
On the other hand if you compile a program that uses null instead of []
you see some differences. In the current dmd compiler returning null is
more efficient. I have seen code where this difference in performance
matters:
int[] foo() {
return [];
}
int[] bar() {
return null;
}
void main() {}
_D4temp3fooFZAi:
L0: push EAX
mov EAX,offset FLAT:_D11TypeInfo_Ai6__initZ
push 0
push EAX
call near ptr __d_arrayliteralTX
mov EDX,EAX
add ESP,8
pop ECX
xor EAX,EAX
ret
_D4temp3barFZAi:
xor EAX,EAX
xor EDX,EDX
ret
Bye,
bearophile
That is a compiler bug isn't it ?
No. [] calls the hook for _d_arrayliteral, whose source is not known at
compile time. Runtime functions cannot be inlined, which will be set in
stone once the runtime is a dynamic library.
-Steve
