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The allowed function parameter and return types are:

  • Double
  • String
  • DateTime -- returns a double to Excel (maybe string is better to return?)
  • Double[] -- if only one column is passed in, takes that column, else first row is taken
  • Double[,]
  • Object
  • Object[] -- if only one column is passed in, takes that column, else first row is taken
  • Object[,]
  • Boolean (bool) -- returns an Excel bool (maybe string is better to return to Excel?)
  • Int32 (int)
  • Int16 (short)
  • UInt16 (ushort)
  • Decimal
  • Int64 (long)

incoming function parameters of type Object will only arrive as one of the following:

  • Double
  • String
  • Boolean
  • ExcelDna.Integration.ExcelError
  • ExcelDna.Integration.ExcelMissing
  • ExcelDna.Integration.ExcelEmpty
  • Object[,] containing an array with a mixture of the above types
  • ExcelReference -- (Only if AllowReference=true in ExcelArgumentAttribute causing R type instead of P)

function parameters of type Object[] or Object[,] will receive an array containing a mixture of the above types (excluding Object[,])

return values of type Object are allowed to be:

  • Double
  • String
  • DateTime
  • Boolean
  • Double[]
  • Double[,]
  • Object[]
  • Object[,]
  • ExcelDna.Integration.ExcelError
  • ExcelDna.Integration.ExcelMissing.Value -- Converted by Excel to be 0.0
  • ExcelDna.Integration.ExcelEmpty.Value -- Converted by Excel to be 0.0
  • ExcelDna.Integration.ExcelReference
  • Int32 (int)
  • Int16 (short)
  • UInt16 (ushort)
  • Decimal
  • Int64 (long)

Otherwise return #VALUE! error

Return values of type object[] and object[,] are processed as arrays of the type object, containing a mixture of the above, excluding the array types.

Special return values​

The following invalid return values, are returned to Excel as indicated

  • Object[0] => #VALUE
  • Object[0.0] => #VALUE
  • String.Empty => ""
  • ExcelEmpty.Value => 0
  • null => #NUM