retrieving the ID of a struct

[vlo...@gmail.com]

What's the proper way to get the ID associated with a struct at runtime? Will accessing this pull in the entire dynamic schema? I'm hoping I can just get the ID with minimal overhead.

Thanks!

[Kenton Varda]

Hi Vitali,

Hmm, what do you mean by "at runtime"? Type IDs are not sent on the wire, so if all you have are some bytes, there's no way to get the type ID.

If you know the type at compile time, you can use `capnp::typeId<MyStructType>()` in code to get the type ID of a struct as a constexpr... but that's compile time, not runtime.

-Kenton

On Wed, Apr 22, 2020 at 5:35 PM <vlo...@gmail.com> wrote:

What's the proper way to get the ID associated with a struct at runtime? Will accessing this pull in the entire dynamic schema? I'm hoping I can just get the ID with minimal overhead.

Thanks!

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[Vitali Lovich]

Sorry. I did mean `capnp::typeId<MyStructType>` rather than looking it up dynamically for a type. Does capnp::typeId cause the entire schema to be pulled in? It looks like it just pulls in EnumInfo<T>::typeId so I'm hoping function/data sections will cause the encoded schema itself to be stripped out.

[Kenton Varda]

Since it's a constexpr, the compiler will evaluate it to an integer at compile-time, so it shouldn't pull in any symbols at all.

-Kenton