Hello,

Are here any differences in creation of dynamic array with known size?

> auto array = new wchar[](111);

and

> wchar[] array;
> array.length = 111;

On Monday, 9 November 2020 at 08:06:54 UTC, Andrey wrote:
> Hello,
>
> Are here any differences in creation of dynamic array with known size?
>
>> auto array = new wchar[](111);
>
> and
>
>> wchar[] array;
>> array.length = 111;

You can check using compiler explorer:
https://godbolt.org/

On Monday, 9 November 2020 at 09:05:58 UTC, Imperatorn wrote:
> On Monday, 9 November 2020 at 08:06:54 UTC, Andrey wrote:
>> Hello,
>>
>> Are here any differences in creation of dynamic array with known size?
>>
>>> auto array = new wchar[](111);
>>
>> and
>>
>>> wchar[] array;
>>> array.length = 111;
>
> You can check using compiler explorer:
> https://godbolt.org/

I don't understand assembly, so this does not tell me anything useful.

Are there any reasons to prefer one over the other? I assume this is what OP is actually asking about.

On Monday, 9 November 2020 at 08:06:54 UTC, Andrey wrote:
> Hello,
>
> Are here any differences in creation of dynamic array with known size?
>
>> auto array = new wchar[](111);
>
> and
>
>> wchar[] array;
>> array.length = 111;

In theory
auto array = new wchar[111]; // or new wchar[](111);
should do less work, but in practice I would guess there will be almost zero difference in speed.

If you need to create new dynamic array with known size you should prefere
auto array = new wchar[111]; // or new wchar[](111);

because it is make much more sense than create empty non initialized array and then set it a length

On Monday, 9 November 2020 at 08:06:54 UTC, Andrey wrote:
> Hello,
>
> Are here any differences in creation of dynamic array with known size?
>
>> auto array = new wchar[](111);
>
> and
>
>> wchar[] array;
>> array.length = 111;

It's the same. If the two are valid then you are in a function. So it's an alloca for the dynamic array payload (8+8 bytes on x86_64) then a LengthExpression that will lead to a GC.malloc, and finally a memset for all the elements default values.

On Monday, 9 November 2020 at 09:05:58 UTC, Imperatorn wrote:
> On Monday, 9 November 2020 at 08:06:54 UTC, Andrey wrote:
>> Hello,
>>
>> Are here any differences in creation of dynamic array with known size?
>>
>>> auto array = new wchar[](111);
>>
>> and
>>
>>> wchar[] array;
>>> array.length = 111;
>
> You can check using compiler explorer:
> https://godbolt.org/

Cool tool!

Array creation disassemble: https://godbolt.org/z/GzxWao