nimforum mirror - A form of dynamic default construction, similar to a constructor. default(T)

hyu1996 (orginal) [2025-10-15T05:10:28+02:00] view original

Due to limitations in Nim, object default values cannot be dynamically generated. I’ve found a workaround for this and wanted to share it with everyone. Currently, I’m using this approach to generate unique IDs for some simple value objects.


# initializer.nim
type
  Initializer[T] = proc (): T {.nimcall.}

converter initializer*[T](initializer: Initializer[T]): T =
  initializer()

# tdemo
# initializer.nim
type
  Initializer[T] = proc (): T {.nimcall.}

converter initializer*[T](initializer: Initializer[T]): T =
  initializer()

# tdemo
import std/oids
import std/monotimes

# import ./initializer

type
  SomeObj = object
    oid: Oid = genOid
    createTime: MonoTime = getMonoTime

echo SomeObj()        # (oid: 68ef0d893d02f403092dc47f, createTime: 2215664448842369)
echo default(SomeObj) # (oid: 68ef0d893d02f403092dc47f, createTime: 2215664448842369)

https://play.nim-lang.org/#pasty=KavNrekg

Perhaps this is just a bug.

Mirror of forum.nim-lang.org

13459 :: A form of dynamic default construction, similar to a constructor. default(T)