nim-package-visible-types

A hacky helper lib for authoring Nim packages with package-level visiblity

What problem does this solve?

https://forum.nim-lang.org/t/4293

How does it work?

Create a private types module for your package. Put all of the types into a single packageTypes block like this:

import
  package_visible_types

packageTypes:
  type
    EthereumNode* = ref object
      networkId*: uint
      chain*: AbstractChainDB
      clientId*: string
      connectionState*: ConnectionState
      keys*: KeyPair
      address*: Address
      rlpxCapabilities: seq[Capability]
      rlpxProtocols: seq[ProtocolInfo]
      listeningServer: StreamServer
      protocolStates: seq[RootRef]
      discovery: DiscoveryProtocol
      peerPool*: PeerPool

    Peer* = ref object
      transport: StreamTransport
      dispatcher: Dispatcher
      lastReqId*: int
      network*: EthereumNode
      secretsState: SecretState
      connectionState: ConnectionState
      remote*: Node
      protocolStates: seq[RootRef]
      outstandingRequests: seq[Deque[OutstandingRequest]]
      awaitedMessages: seq[FutureBase]

    OutstandingRequest = object
      id: int
      future: FutureBase
      timeoutAt: uint64

    ...

Even though some of the types and fields are private in the module above, packageTypes will automatically define public accessors for them (intended for your private use from the package). Furthermore, you can easily re-export the public definitions in the following way:

import
  private/types
  
types.forwardPublicTypes

The scheme is currently limited to types, because private modules consisting of procs are already forwarded relatively easy with templates.

How does it work exactly?

1. Private types are made public, but not added to the list of forwarded types.
2. Templates are added for the private fields (read-only and var-like getters, setters, etc)

Are there any limitations?

Unfortunately, yes.

1. It's not possible to use the object constructor syntax for objects that carry private fields. As a work-around, the library defines init templates for all of the types:

var r =  OutstandingRequest.init(id = result,
                                 future = responseFuture,
                                 timeoutAt = timeoutAt)

2. If an object stores a function pointer in a field, Nim will confuse the function pointer invocation with an application of the accessor template (resulting in an error). You can work-around the problem like this:

let result = (obj.someFuncPtr)(param, param)

3. The accessor templates will sometimes introduce various other general overloading issues in the context of other templates and generic functions.