.. worms:

  [8.7a2] % namespace eval foo {proc : {} {namespace current}}
  can't create procedure ":" in non-global namespace with name starting with ":"
  [8.7a2] % namespace eval foo {proc x {} {namespace current}}
  [8.7a2] % namespace eval foo {rename x :}
  [8.7a2] % namespace eval foo :
  ::foo

  [8.7a2] % oo::class create {}
  object name must not be empty
  [8.7a2] % oo::class create :
  ::
  [8.7a2] % {} create {}
  object name must not be empty
  [8.7a2] % {} create :
  Segmentation fault (core dumped)