A undef is used to express values that do not exists, or which have no valid path. The value undef occurs whenever a carbon record is queried for a non-existing path using a dot path expression.

Carbon TypeDescriptionSizenull-ValueMarker
undefabsence of data (structure-defined)0none[N]

Encoding as Field Value

Carbon File snippet

[[] [N] []] 

Note that undef does not match to a Json null, use a Carbon null type instead. For more, see Section Nulls.

Since there is no mapping from a Carbon undef value to a Json value for Json-formatted output, a undef value is formatted as a Json-string prefixed with _.

Json File snippet


Note that this is a uni-directed mapping from Carbon files to Json files. The opposite direction, i.e., mapping from "_undefined" to undef, is not defined.

Encoding as Column Value

undef values are not supported for column containers.