C++: How to "cast" a Capability::Client to AnyPointer

[Michael Berg]

Hello,

interface A(T) {

    value @0 () -> (val :T);

}

is there a way to get from a capnp::Capability::Client to a capnp::AnyPointer? 

I'm struggling with some generic schema where I'm implementing "A::Server" which holds an AnyPointer member field to store a value of some type T. An instance of A will later be returned to a client which can then get the value via calling the "value" method. The value to be stored in A can for instance either be a list of Capability::Client or a just a Capability::Client. So when I want to instantiate A I got (e.g. as a parameter to the method) a Capability::Client not an AnyPointer. 

So my problem is, that I can easily get a Capabilty::Client from an AnyPointer via AnyPointer::getAs<some Interface>(), but I find no way to get from a Capabilty::Client to an AnyPointer which I need in order to create an instance of A (in my C++ code). I have the feeling that I'm missing something very obvious.

Can somebody help?

Thank you and best regards

Michael

[Kenton Varda]

Hi Michael,

The thing about AnyPointer is that it's not just a pointer to a value -- it's a (native) pointer to a (capnp) pointer, the latter of which has to exist within some larger message.

The right way to initialize an AnyPointer, then, is more like how you'd initialize a nested struct -- you start with the parent object's Builder and call getVal() to get an AnyPointer::Builder, then you call setAs<whatever>(value) on that, like:

  context.getResults().getVal().setAs<SomeInterface>(capClient);

Does that help?

-Kenton

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[Michael Berg]

Hello Kenton,

yes, this helped. Thanks a lot for the help and quick reply. 

Cheers, Michael

On Tuesday, August 27, 2019 at 5:50:18 PM UTC+2, Kenton Varda wrote:

Hi Michael,

The thing about AnyPointer is that it's not just a pointer to a value -- it's a (native) pointer to a (capnp) pointer, the latter of which has to exist within some larger message.

The right way to initialize an AnyPointer, then, is more like how you'd initialize a nested struct -- you start with the parent object's Builder and call getVal() to get an AnyPointer::Builder, then you call setAs<whatever>(value) on that, like:

  context.getResults().getVal().setAs<SomeInterface>(capClient);

Does that help?

-Kenton

On Tue, Aug 27, 2019 at 7:09 AM Michael Berg <suuri...@gmail.com> wrote:

Hello,

interface A(T) {

    value @0 () -> (val :T);

}

is there a way to get from a capnp::Capability::Client to a capnp::AnyPointer? 

I'm struggling with some generic schema where I'm implementing "A::Server" which holds an AnyPointer member field to store a value of some type T. An instance of A will later be returned to a client which can then get the value via calling the "value" method. The value to be stored in A can for instance either be a list of Capability::Client or a just a Capability::Client. So when I want to instantiate A I got (e.g. as a parameter to the method) a Capability::Client not an AnyPointer. 

So my problem is, that I can easily get a Capabilty::Client from an AnyPointer via AnyPointer::getAs<some Interface>(), but I find no way to get from a Capabilty::Client to an AnyPointer which I need in order to create an instance of A (in my C++ code). I have the feeling that I'm missing something very obvious.

Can somebody help?

Thank you and best regards

Michael

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