Delphi Basics : Variant command

Delphi Basics
Variant
Type A variable type that can hold changing data types System unit
type Variant;
Description
The Variant data type provides a flexible general purpose data type.
It can hold anything but structured data and pointers.
But use with care - there are penalties in performance, potentials for run time errors and poor code clarity when using Variants.
Use VarType in conjunction with VarTypeMask to determine the curent data types a Variant is set to.
Variants are useful in very specific circumstances, where data types and their content are determined at run time rather than at compile time.
Notes
Variant strings cannot be indexed.
Related commands
Null A variable that has no value
PVariant Pointer to a Variant value
Example code : Illustrating a few Variant assignments and the resulting data types var
myVar : Variant;
begin
// Assign various values to a Variant
// and then show the resulting Variant type
ShowMessage(‘Variant value = not yet set‘);
ShowBasicVariantType(myVar);
// Simple value
myVar := 123;
ShowMessage(‘Variant value = 123‘);
ShowBasicVariantType(myVar);
// Calculated value using a Variant and a constant
myVar := myVar + 456;
ShowMessage(‘Variant value = 123 + 456‘);
ShowBasicVariantType(myVar);
myVar := ‘String ‘+IntToStr(myVar);
ShowMessage(‘Variant value = String 579‘);
ShowBasicVariantType(myVar);
end;
// Show the type of a variant
procedure TForm1.ShowBasicVariantType(varVar: Variant);
var
typeString : string;
basicType  : Integer;
begin
// Get the Variant basic type :
// this means excluding array or indirection modifiers
basicType := VarType(varVar) and VarTypeMask;
// Set a string to match the type
case basicType of
varEmpty     : typeString := ‘varEmpty‘;
varNull      : typeString := ‘varNull‘;
varSmallInt  : typeString := ‘varSmallInt‘;
varInteger   : typeString := ‘varInteger‘;
varSingle    : typeString := ‘varSingle‘;
varDouble    : typeString := ‘varDouble‘;
varCurrency  : typeString := ‘varCurrency‘;
varDate      : typeString := ‘varDate‘;
varOleStr    : typeString := ‘varOleStr‘;
varDispatch  : typeString := ‘varDispatch‘;
varError     : typeString := ‘varError‘;
varBoolean   : typeString := ‘varBoolean‘;
varVariant   : typeString := ‘varVariant‘;
varUnknown   : typeString := ‘varUnknown‘;
varByte      : typeString := ‘varByte‘;
varWord      : typeString := ‘varWord‘;
varLongWord  : typeString := ‘varLongWord‘;
varInt64     : typeString := ‘varInt64‘;
varStrArg    : typeString := ‘varStrArg‘;
varString    : typeString := ‘varString‘;
varAny       : typeString := ‘varAny‘;
varTypeMask  : typeString := ‘varTypeMask‘;
end;
// Show the Variant type
ShowMessage(‘Variant type  = ‘+typeString);
end;
Show full unit code
Variant value = not yet set
Variant type  = varEmpty
Variant value = 123
Variant type  = varByte
Variant value = 123 + 456
Variant type  = varInt64
Variant value = String 579
Variant type  = varString
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