Variant Type

Variant Type

Variant is a data type in certain programming languages, particularly Visual Basic and C++ when using the Component Object Model.

In Visual Basic (and Visual Basic for Applications) the Variant data type is a tagged union that can be used to represent any other data type (for example, integer, floating-point, single- and double-precision, object, etc.) except fixed-length string type and record types. In Visual Basic any variable, not declared explicitly or the type of which is not declared explicitly, is taken to be a variant.

While the use of not explicitly declared variants is not recommended, they can be of use when the needed data type can only be known at runtime, when the data type is expected to vary, or when optional parameters and parameter arrays are desired. In fact, languages with a dynamic type system often have variant as the only available type for variables.

Among the major changes in Visual Basic .NET, being a .NET language, the variant type was replaced with the .NET object type. There are similarities in concept, but also major differences, and no direct conversions exist between these two types. For conversions, as might be needed if Visual Basic .NET code is interacting with a Visual Basic 6 COM object, the normal methodology is to use .NET marshalling.

In unrelated usage, variant type is also used to refer to an algebraic data type (comparable to a tagged union), whose constructors are often called variants. In languages such as OCaml and Haskell, this kind of variant type is the standard language building block for representing many data structures.