Unsigned integers could not be used as array indexes.

[cheatfate]

This code could not be compiled, because UnsignedConst is unsigned integer,
with error Error: ordinal type expected

const
  UnsignedConst = 1024'u
type
  SomeObject* = object
    s1: array[UnsignedConst, uint32]

[bluenote10]

According to the manual it is by design that unsigned integers are not ordinal. The question why they are not was also raised in a related issue #6620.

[Araq]

That's true but array indexing does not have to be bound by the "ordinal type" constraint.