Passing params as struct using derive-macro

[ababo]

Is there a way to pass method params through single struct (for sake of extensibility and flexibility), i.e. something like

#[rpc]
pub trait ServerApi {
    fn foo(&self, params: FooParams) -> Result<FooReply>;
}

struct FooParams {
    bar: String,
}

So now I can call {"jsonrpc":"2.0","id":123,"method":"foo","params":{"bar": "buzz"}}.

[ababo]

Moreover even without the derive macro there's no way to handle named params without Map->JSON->struct conversion which is inefficient and ugly. Did I miss something?