what size should an empty object be?

[theSherwood]

Should empty objects be of size 0? Maybe in some contexts that won't even work.

Example

type
  Empty = object
  Wrapper*[K, V] = object
    node*: (K, V)
echo sizeof(Empty)
echo sizeof(Wrapper[uint8, Empty])

Actual Output

1
2

Expected Output

0
1

Possible Solution

Additional Information

References

[zerbina]

It's possible to implement empty objects/tuples/arrays having a size of 0, but I personally don't think it's worth the added compiler/language complexity.

[starsiderfox]

It looks like there's already a type of size 0 that add nothing to any structure it's part of.

type Empty = distinct array[0, byte]

It must be based on an 8 bit type so it doesn't alter the layout (e.g. if it's an array[0,int64] it will instead force any adjacent type into 8 byte size and alignment).

However seqs seem to allocate 1 byte for each Empty. Similarly, tuples and objects that only contain tuples are equivalent to empty tuples and objects, all of which have size 1.

[zerbina]

It looks like there's already a type of size 0 that add nothing to any structure it's part of.

type Empty = distinct array[0, byte]

The size being reported as 0 is a compiler bug -- in the generated code, arrays with a length <= 0 always have a length of 1.

In any case, there's been discussion about a unit type since this question was originally asked. The unit type will most likely end up becoming the type to use for fields/locals when they should not take up any space nor alter alignment requirements.