Fully async snell controller action

action.rb

def update
  user = User.find(1)
  if user.update_attributes(params[:user])
    respond_with(@user)
  else
    respond_with(@user.errors, :status => :unprocessable_entity)
  end
end

action.swift

  func update() -> Promise<Response> {
    // Swift's current level of suck at type inference and closures makes this more verbose than
    // would otherwise be expected. It should be solvable in llvm and hopefully the situation improves.
    return User.find(1)
      .then({ (user:Repository) -> Promise<Response> in
        let user = user as! User
        return user.update_attributes(["name": "Test"])
          .then({ (valid:Bool) -> Response in
            if valid {
              return Response(status: 200, body: "User updated")
            } else {
              return Response(status: 422, body: "Validation errors")
            }
          })
      })
  }

Looks sensible, but yes, verbose.

And I'm wondering how to expose hooks to reduce the boilerplate and handle common failures. For example, implicit in the Rails version is rescuing ActiveRecord::RecordNotFound with a sensible 404 -- we're not even capturing that here.