Forbid dynamic arrays in boolean evaluation contexts

[Steven Schveighoffer]

On Tue, 26 Mar 2013 23:21:35 -0400, deadalnix <deadalnix at 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