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VarIsNull

function VarIsNull(const V: Variant): Boolean;

Example​

procedure ScriptEvent(var Value: variant);
var
  Candidate: Variant;
begin
  Candidate := Null;
  Value := VarIsNull(Candidate); // True
end;

Usage​

VarIsNull tests whether a Variant contains exactly the explicit Null state.

Parameters and result

ItemTypeDescription
VVariant (const)Value to inspect without conversion. Nested Variant/by-reference Variant indirection is resolved for this predicate.
ResultBooleanTrue only when the resolved stored type is varNull; otherwise False.

Additional Technical Info​

VarIsNull returns True only when V contains the Variant Null state represented by varNull. Null conventionally represents an explicitly unknown or missing value; it is different from an unassigned Variant.

The example is fictional and source-reviewed only.

Implementation and behaviour

The modified PascalScript runtime registers Delphi System.Variants.VarIsNull directly. Delphi follows the underlying Variant data and compares its type code with varNull.

The function does not apply Delphi's Null comparison or conversion policies, so it is the reliable way to branch before an operation that may propagate Null or raise under strict Null conversion. It also does not treat Empty, a nil interface, empty text, zero, false or a blank database field already converted to text as Null.

VarToStrDef and VarToWideStrDef use this exact Null test before selecting their fallback. Their defaults therefore do not apply to Empty or to an otherwise invalid conversion.

Side effects, errors, performance and concurrency

The routine is a constant-time type check with no conversion, allocation, I/O, global-state mutation or ordinary exception path. As with other managed values, do not read and mutate the same Variant storage concurrently without coordination.

Related entries

  • VarIsEmpty tests the distinct Empty/Unassigned state.
  • VarIsClear provides the broader no-usable-value test.
  • VarToStrDef substitutes caller text only when this predicate is true.

External references

Created 2026-07-15