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IsNullorEmpty

Function IsNullorEmpty( const aValue : variant) : boolean

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := IsNullorEmpty(Null);
end;

Usage​

IsNullorEmpty tests whether a Variant is null, empty, clear or reduces to empty trimmed text under Velox's rules.

Parameters

NameTypeDescription
aValueVariant, constValue to classify. Conversion is attempted only after the explicit state, string and numeric branches.

Returns

Input categoryResult
VarIsNull, VarIsEmpty or VarIsClearTrue
String VariantWhether Trim(aValue) = ''
Numeric Variant, including numeric zeroFalse
Other Variant typeWhether Trim(VarToStr(aValue)) = '', if conversion succeeds

Behaviour

Null, unassigned/Empty and clear values are deterministically empty under their Velox Variant predicates. Empty and whitespace-only string Variants are empty after Velox Trim. Numeric values are always considered nonempty, regardless of magnitude.

Other types are converted with Velox VarToStr, trimmed and compared with the empty string. This fallback makes the result dependent on whether and how that Variant type supports string conversion.

Errors

The explicit state and numeric checks avoid conversion errors for those categories. Other values can raise a Variant conversion or property-access error, and the function does not catch it.

Additional Technical Info​

IsNullorEmpty classifies a Variant through explicit Null/Empty/clear checks, a trimmed-string branch, a numeric branch and finally a string-conversion fallback. It is Velox's documented absence predicate; numeric zero is deliberately considered present.

The example returns True through the explicit Null predicate. It is source-reviewed and is not executed by the documentation workflow.

Implementation

The PascalScript import calls vxCommonString.IsNullorEmpty directly. The branch order is significant: type predicates run before any direct equality or general conversion, string values are trimmed, and all numeric values exit False without formatting.

Edge cases and quirks

  • Numeric zero is False (not empty). Use a separate zero rule when zero is also absent for a particular field.
  • False is not explicitly an empty state. Its fallback string representation is normally nonempty, so it returns False.
  • String trimming occurs only after the Variant is identified as string. The exact characters removed are those recognised by the deployed Delphi Trim implementation.
  • Variant arrays, interfaces, dispatch values, custom variants and other complex values are not automatically empty. VarToStr can return text or raise because no conversion exists.
  • A string containing an embedded null character is still a Delphi string and is not truncated by this implementation; trimming/comparison use string length.
  • Process-wide Variant string-conversion settings can influence the fallback for applicable types.

Side effects

The function does not mutate the Variant. A custom Variant type could execute its own conversion logic when VarToStr is called; any side effects of that custom handler are outside this wrapper's control.

Performance and concurrency

State and numeric checks are constant-time. String trimming/conversion is proportional to produced text and can allocate. The wrapper is re-entrant, but custom Variant handlers and global conversion rules can have their own concurrency constraints.

Remarks

This function is safer for absence testing than direct Variant = Null, but its name still represents Velox's particular policy. Define separately whether numeric zero, Boolean false, an empty array or an inactive object should count as absent in the owning configuration field.

Related entries

  • IsNullorZero uses direct Variant equality and has different Null/coercion semantics.
  • CheckBoolean converts a present Variant to Boolean.
  • Testing values distinguishes common Variant states.

External references

Created 2026-07-15