Generic Router Implementation

[mossid]

Ref: #3880 (comment)

We now have three router logic:

Tx Router: https://github.com/cosmos/cosmos-sdk/blob/develop/baseapp/router.go
Query Router: https://github.com/cosmos/cosmos-sdk/blob/develop/baseapp/queryrouter.go
Proposal Handler: (PR not merged yet)

We need to abstract out this logic, we expect the number of multipurpose modules(like governance proposal) will increase. Two possible implementations are go generate and reflect(https://golang.org/pkg/reflect/#Value.Call). AFAIK go generate is recommended to avoid in our codebase, and reflection is inefficient. Is there a better way to improve?

[alexanderbez]

Under the hood the router is just a simple map, no? We can have a generic router that is of type map[string]interface{} and enforce the caller to make sure the returning values are the correct type. This is essentially identical to go's container/list.

[jackzampolin]

This is a great thing for dev ux when building on the SDK. I think this is something we might want to look at while splitting gaia out of the SDK

[tac0turtle]

I think this is more or less completed with the migration to protobuf. We no longer require users to create switch statements since the protobuf service is registered now.