Double unary operator (--) does not coerce dynamic array results correctly

[JHirche]

EPPlus usage

Commercial use (I have a commercial license)

Environment

Windows 11

Epplus version

8.4.2

Spreadsheet application

Excel (Office 365)

Description

Hello,

it seems that the double unary operator (--) does not correctly coerce values when applied to dynamic array expressions.

Example

Consider the following worksheet:

	A	B	C	D	E
1	TRUE	=A1	=--(A1)	=A1:A2	=--(A1:A2)
2	FALSE	=A2	=--(A2)

After calling Calculate() on the Workbook, the following results are produced:

	A	B	C	D	E
1	TRUE	TRUE	1	TRUE	0
2	FALSE	FALSE	0	FALSE	0

Expected behavior

In Excel (Microsoft 365), the formula =--(A1:A2) (Column E) spills and evaluates to:

		E
1	...	1
2	...	0

So cell E1 should contain 1, not 0.

The double unary operator works correctly for scalar values (=--(A1) and =--(A2)), but does not behave correctly when applied to a range/dynamic array expression.

Question

Is the double unary operator officially supported by the formula engine?

It is not listed as a function in the documentation, but the attached logger does not indicate that it is unsupported either.

Code

using var package = new ExcelPackage(new FileInfo("example.xlsx"));

using var workbook = package.Workbook;
workbook.FormulaParserManager.AttachLogger(new FileInfo("example_log.txt"));
workbook.Calculate();

package.SaveAs(new FileInfo("example_new.xlsx"));

Log

=================================
Timestamp: 25.02.2026 08:50:04

Starting formula calculation.

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!B1	True	Boolean

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!C1	1	Decimal

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!D1	OfficeOpenXml.FormulaParsing.Ranges.RangeInfo	ExcelRange

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!E1	OfficeOpenXml.FormulaParsing.Ranges.InMemoryRange	ExcelRange

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!B2	False	Boolean

=================================
Timestamp: 25.02.2026 08:50:04

Set value in Cell	Sheet1!C2	0	Decimal

=================================
Timestamp: 25.02.2026 08:50:04

Calculation done...number of cells parsed: 8

Thank you for your help.

[swmal]

@JHirche Thanks for reporting this, fix will be included in the next version.

[JHirche]

Thanks for the quick response.