RAD Studio VCL Reference
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TCustomVariantType is the base class for Delphi custom variant types.
TCustomVariantType = class(TObject, IInterface);
class TCustomVariantType : public TObject, public IInterface;
Variants
Use TCustomVariantType to define new data types for Delphi Variants. TCustomVariantType descendants do not represent the Variants themselves. Rather, they act as utility classes that the custom Variants call on to perform their operations.
To create a Variant type,
1.Map the storage of the Variant's data on to the TVarData record.
2.Write a method that creates instances of your custom Variant. This fills in the Variant's data as defined in step 1.
3.Declare a class that descends from TCustomVariantType.
4.Implement all required behavior (including type conversion rules) in the new class. This involves overriding the appropriate virtual methods (typically BinaryOp, UnaryOp, CompareOp or Compare, Cast, CastTo, Clear, Copy, IsClear, LeftPromotion, and RightPromotion).
5.In the initialization section of the unit that defines your TCustomVariantType descendant, create an instance of your class. When you instantiate your object, it automatically registers itself with the Variant-handling system so that the new Variant type is enabled.
6.In the finalization section of the unit that defines your TCustomVariantType descendant, free the instance of your class. This automatically unregisters the Variant type.
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