Hmm, can't that function be equivalently written as:
myT* refPtr(myT& ref) { return &ref; }
?
On Wed, Sep 4, 2019 at 3:51 PM Stefan Kaps <[email protected]> wrote:
> Oh, very cool. I had not yet stumbled upon it. This is definitly better
> than my solution, as it most likely won't generate any code where it's not
> needed.
>
> Just an hour ago I wrote my own little hacky thing: a simple asm function
> that returns its first parameter.
>
> extern "C" {
> myT *refPtr( myT & );
> };
>
> As the asm simply does
> mov rax, rcx
> ret
>
> Works fine as we know under the hood references are pointers. I would
> hope the CPU itself would optimize around the call-ret, seeing only one uOp
> being produced before reaching the "ret".
>
> Am Donnerstag, 5. September 2019 00:43:18 UTC+2 schrieb Kenton Varda:
>>
>> Hi Stefan,
>>
>> A Builder already acts like a pointer: You can copy it by value, and the
>> copy manipulates the same underlying message.
>>
>> If you just want to express the type "capnp::Builder or null", then I
>> suggest using `kj::Maybe<capnp::Builder>`, which serves exactly this
>> purpose. A `kj::Maybe<T>` can be assigned to any `T` or to `nullptr`. You
>> can unpack a Maybe with `KJ_IF_MAYBE()`. Check out the comments in
>> `kj/commen.h` and copious examples throughout the KJ and Cap'n Proto source
>> code to learn more.
>>
>> -Kenton
>>
>> On Wed, Sep 4, 2019 at 11:10 AM Stefan Kaps <[email protected]> wrote:
>>
>>> Hi,
>>>
>>> i would like to use pointers to builders in my exporter, so I can pass
>>> nullptr in case of "please simply do a check, but do not build
>>> capnp-data". Is this possible at all?
>>>
>>> If not, are there any suggestions you have for me how to provide such
>>> functionality?
>>>
>>> Thanks a lot in advance,
>>> Stefan
>>>
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