A Variant is a union of the built-in types.

The structure of a Variant is shown in Table 20.

Table 20 – Variant Binary DataEncoding


Data Type




The type of data encoded in the stream. A value of 0 specifies a NULL and that no other fields are encoded.The mask has the following bits assigned:


Built-in Type Id (see Table 1).


True if the ArrayDimensions field is encoded.


True if an array of values is encoded.

The Built-in Type Ids 26 through 31 are not currently assigned but may be used in the future. Decoders shall accept these IDs, assume the Value contains a ByteString or an array of ByteStrings and pass both onto the application. Encoders shall not use these IDs.

The ArrayDimensions field shall only be present if the number of dimensions is 2 or greater and all dimensions have a length greater than 0.



The number of elements in the array.

This field is only present if the array bit is set in the encoding mask.

Multi-dimensional arrays are encoded as a one-dimensional array and this field specifies the total number of elements. The original array can be reconstructed from the dimensions that are encoded after the value field.

Higher rank dimensions are serialized first. For example, an array with dimensions [2,2,2] is written in this order:

[0,0,0], [0,0,1], [0,1,0], [0,1,1], [1,0,0], [1,0,1], [1,1,0], [1,1,1]

If one or more dimensions has a length <= 0 then the ArrayLength is 0.



The value encoded according to its built-in data type.

If the array bit is set in the encoding mask, then each element in the array is encoded sequentially. Since many types have variable length encoding each element shall be decoded in order.

The value shall not be a Variant but it could be an array of Variants.

Many implementation platforms do not distinguish between one dimensional Arrays of Bytes and ByteStrings. For this reason, decoders are allowed to automatically convert an Array of Bytes to a ByteString.



The number of dimensions.

This field is only present if the ArrayDimensions flag is set in the encoding mask.



The length of each dimension encoded as a sequence of Int32 values

This field is only present if the ArrayDimensions flag is set in the encoding mask. The lower rank dimensions appear first in the array.

All dimensions shall be specified and shall be greater than zero..

If ArrayDimensions are inconsistent with the ArrayLength then the decoder shall stop and raise a Bad_DecodingError.

The types and their identifiers that can be encoded in a Variant are shown in Table 1.