Variant

A Variant is a union of all built-in data types including an ExtensionObject. Variants can also contain arrays of any of these built-in types. Variants are used to store any value or parameter with a data type of BaseDataType or one of its subtypes.

Variants can be empty. An empty Variant is described as having a Null value and should be treated like a NULL column in a SQL database. A Null value in a Variant may not be the same as a Null value for data types that support Nulls such as Strings. For this reason, all DataEncodings shall preserve this distinction when encoding Variants.

Variants can contain arrays of Variants but they cannot directly contain another Variant.

Variants cannot contain arrays of Bytes. Parameters that are defined as arrays of Bytes are stored as ByteStrings in a Variant.

DiagnosticInfo type only has meaning when returned in a response message with an associated StatusCode. As a result, Variants cannot contain instances of DiagnosticInfo.

Variables with a DataType of BaseDataType are mapped to a Variant, however, the ValueRank and ArrayDimensions Attributes place restrictions on what is allowed in the Variant. For example, if the ValueRank is Scalar then the Variant may only contain scalar values.