Improve type check of keys

[kuy]

Is your feature request related to a problem? Please describe.

In a table which has both partition key and sort key, rustc doesn't raise errors if I forget to call sort_key(...) method to pass sort key.

Describe the solution you'd like

raiden-derive could generate more precise signatures like fn get(&mut self, key: (K, K)) where K: IntoAttribute + Send instead of fn get(&mut self, key: impl IntoAttribute + Send) base on given definition of the struct.

Want to discuss

• Strict type check of key
  • e.g. client.get(2020) yields compile errors => Strict type checking of keys #47

Abstract Key

In batch_get op, there are lots of conditional code generations like below.

https://github.com/raiden-rs/raiden/blob/94a77a238405acca7a048d397a6347297b7768b1/raiden-derive/src/ops/batch_get.rs#L73-L90

I want to reduce repeat by defining an abstract type for keys. This means that the type consists of impl IntoAttribute and (impl IntoAttribute, impl IntoAttribute). If I define the abstract type using enum, it looks like below.

enum Key {
  Pk(impl IntoAttribute),
  PkSk((impl IntoAttribute, impl IntoAttribute)),
}

However, this is annoying in its representation.

let keys = vec![("aaa", 2019), ("bbb", 2020), ("ccc", 2021)]; // looks naturally

let keys = vec![PkSk("aaa", 2019), PkSk("bbb", 2020), PkSk("ccc", 2021)]; // umm....

So finally, I stopped this approach.

[kuy]

Tackle after #14