c-s: params wrapper

[muzarski]

Motivation

Before the changes, a lot of common logic (and fields) would be repeated in implementations of Param trait. I found it annoying when implementing yet another type of parameters (DistributionParam - https://github.com/scylladb/cql-stress/pull/48) to repeat the same boilerplate code.

Simple examples:

• required, prefix, satisfied, desc fields used by both SimpleParam and MultiParam
• getters and setters for the fields in Param trait - the exact same implementations for both types of parameters
• common parsing logic - e.g. check if user-provided argument starts with prefix.

This PR introduces a new generic type ParamWrapperImpl<P: Param> which wraps the Param implementations. The logic shared between all of the types of parameters is extracted to the wrapping type.

Changes

• Introduced generic ParamWrapperImpl<P: Param> type which wraps the common logic of the parameters
• Introduced ParamWrapper trait implemented (once) by all of the generic ParamWrapperImpl types. This trait is needed so we can store both ParamWrapperImpl<SimpleParam> and ParamWrapperImpl<MultiParam> in common collections used by the parser.
• Extracted the shared logic from Param implementations to ParamWrapperImpl
• Changed ParamCell type used by the parser from Rc<RefCell<dyn Param>> to Rc<RefCell<dyn ParamWrapper>>. Adjusted usages of the type.

Notes

Please review this PR before https://github.com/scylladb/cql-stress/pull/48, since the options implemented in the mentioned PR base on the changes introduced by this PR.

[muzarski]

v2:

• renamed:
  • trait ParamWrapper -> GenericParam
  • struct ParamWrapperImpl -> TypedParam
  • trait Param -> ParamImpl
• thinned out docstring comments for the types. Especially removed the references to specific ParamImpl implementations in the comments
• Adjusted commit messages to the renamed types

[muzarski]

v3: rebased on top of master

[muzarski]

@piodul should I squash some of the commits (e.g. porting fields from ParamImpl implementations to TypedParam) before mergning?

[piodul]

@piodul should I squash some of the commits (e.g. porting fields from ParamImpl implementations to TypedParam) before mergning?

No, I think the commits are fine as they are right now.