childCount

Number of top-level children: fields for an object, elements for an array, 0 for a scalar.

The one counter that answers for every shape. elementCount and fieldCount stay, and stay throwing, because their job is to assert the shape; this one's job is to let a caller who does not know the shape ask anyway, which is what summarising a value needs. It is one branch over those two answers rather than a third definition of either.

The branch is on basicType rather than kind, deliberately: a primitive whose type id this build does not know still has no children, and that answer never depended on the byte this build cannot read — so it is not a default invented for unknown data, it is an answer that never needed it. Ask kind if you want the failure.

O(1) for every shape.

Throws