Skip to main content

IsNullorZero

function IsNullorZero(const aValue: variant): boolean

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := IsNullorZero(0);
end;

Usage​

Use IsNullorZero only when a controlled Variant is expected to contain an ordinary numeric value and exact zero is the condition of interest.

Do not rely on it for deterministic Null handling or as a text parser. Test VarIsNull or VarIsEmpty explicitly, convert the remaining value to the required numeric type, and use IsZero or IsZeroEpsilon when floating-point tolerance is needed.

Parameters

NameTypeDescription
aValueVariant, constValue compared first with Null and, when required, with integer zero.

Returns

The intended result is True when either direct Variant comparison is true; otherwise False. For ordinary numeric zero/nonzero inputs this is straightforward. Null, text and other Variant types require the qualifications below.

Behaviour

Integer and floating Variant zero values normally compare equal to zero; nonzero numeric values normally return False. Other types may be coerced by Velox for the comparison or may raise.

Direct equality with Null is governed by Velox's process-wide NullEqualityRule and related Variant settings. It is not equivalent to testing VarIsNull(aValue), so the function must not be used where deterministic Null classification is safety-critical without verifying the host settings.

Errors

Direct Variant equality can raise type-cast, invalid-operation or invalid-null exceptions. They are not caught or translated.

Usage notes

For a robust nullable numeric field, first use VarIsNull/VarIsEmpty according to the field contract, then convert through an explicit numeric parser and compare with either exact or tolerant zero as appropriate. That sequence makes errors and accepted input types visible.

Additional Technical Info​

IsNullorZero returns the result of comparing a Variant directly with Null or numeric zero. The example uses a numeric Variant and returns True; it is source-reviewed and is not executed by the documentation workflow.

This wrapper is concise but does not use the explicit Variant predicates used by IsNullorEmpty. Its Null and coercion behaviour is therefore controlled by Delphi's Variant comparison rules.

Implementation

The complete Velox condition is:

(aValue = Null) or (aValue = 0)

This condition is inside a native Delphi function, not compiled from the calling PascalScript expression. The Delphi Boolean-evaluation setting used to build Velox determines whether its second comparison is skipped after a true first result. In either case, the first operation itself is a direct Variant equality.

Edge cases and quirks

  • A Null Variant can produce a result or exception according to Delphi's current Null comparison/conversion rules. The function does not force Null to True with VarIsNull.
  • Numeric-looking strings may be coerced to a number, while other strings can raise a Variant type-cast error. Do not use this as a text parser.
  • Empty, False, dates, custom variants, arrays and interfaces have type-specific coercion/comparison paths. No blanket zero-like guarantee is implemented.
  • Floating values very close to zero but not exactly equal do not receive an epsilon. Use IsZero or IsZeroEpsilon for tolerant floating comparison.
  • A NaN numeric Variant does not compare equal to zero.
  • Because two different comparisons are hidden behind one Boolean, an exception does not identify a business classification; it is a Variant operation failure.

Side effects

The wrapper does not mutate the Variant. Custom Variant comparison handlers can execute type-specific code outside the wrapper.

Performance and concurrency

Ordinary scalar comparisons are constant-time. The function is re-entrant, but results can depend on process-wide Variant rules and custom Variant handlers.

Related entries

  • IsNullorEmpty performs explicit state predicates and treats numeric zero as present.
  • IsZero uses Delphi's default floating tolerance.
  • IsZeroEpsilon uses an explicit floating tolerance.
  • Testing values explains safe Variant checks.

External references

Created 2026-07-15