type CommandId = enum
cmdSearch
cmdDownload
type Command = object
case id: CommandId
of cmdSearch:
opts: SearchOpts
of cmdDownload:
opts: DownloadOpts # Error: attempt to redefine: 'v'
And note that the type must be explicit, no generics allowed. The reason for that being that you must know the explicit field at compileTime so you can link the appropriate procs to it.
Keep in mind that "id" is a runtime field. You can't know at compileTime what it'll be.
So if you have
proc doThing(x: SearchOpts) = echo "search"
proc doThing(x: DownloadOpts) = echo "download"
command.opts.doThing()
It does if you have the same type
type CommandId = enum
cmdSearch
cmdDownload
type Command = object
case id: CommandId
of cmdSearch, cmdDownload:
opts: int
Otherwise, there are several RFCs related to variants, sum types and ADTs:
at the very least.
Also @Araq has been working on a new design of ADTs in the past week.