Implementing generic servers using pycapnp

[Vaci]

Given a generic Capnproto interface, such as:

interface Foo(X)

{

    bar @0 (baz :X);

}

How would one implement a server for Foo using pycapnp?

The following python code doesn't work, presumably as Foo.Server is not a concrete type:

class MyFoo(Foo.Server):

    def bar_context(self, ctx, **kwargs):

         pass

When I attempt to pass my server as an interface parameter, I get the error:

"failed: expected capability.getSchema(),extends(interfaceType); Value type mismatch."

I'd be happy to use a Foo(Any).Server, if that was all I could get...

Vaci

[Kenton Varda]

Hi Vaci,

I suspect pycapnp currently lacks support for specifying generic type parameters. You might want to file an issue on pycapnp's github about that.

However, I suspect you can work around it by defining the type specializations you need in a .capnp file (which could be a private file used by your server), like:

    interface FooMyType extends(Foo(MyType)) {}

    # Extend FooMyType in Python when you really want to extend Foo(MyType).

    interface FooAny extends(Foo) {}

    # Extend FooAny in Python when you really want to implement a generic Foo interface.

-Kenton

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[Vaci]

Hi Kenton,

Thanks, that's exactly the solution I came up with!

Regards,

Vaci

PS On an unrelated note,I've found ekam to be a really neat tool!