CriteriaOperator GetCriteria(
    params CriteriaOperator[] operands
)

Function GetCriteria(
    ParamArray operands As CriteriaOperator()
) As CriteriaOperator

public class MyConcatFunction : ICustomFunctionOperatorBrowsable, ICustomFunctionOperatorFormattable,
    ICustomCriteriaOperatorQueryable {
    const string FunctionName = "MyConcat";
    // ...

    public CriteriaOperator GetCriteria(params CriteriaOperator[] operands) {            
        if(operands == null || operands.Length != 1 || !(operands[0] is MemberInitOperator)) 
            throw new ArgumentException(FunctionName);
        CriteriaOperatorCollection operandCollection = new CriteriaOperatorCollection();
        foreach(XPMemberAssignment operand in ((MemberInitOperator)operands[0]).Members) {
            operandCollection.Add(operand.Property);
        }
        return new FunctionOperator(FunctionName, operandCollection);
    }
}

Public Class MyConcatFunction
    Implements ICustomFunctionOperatorBrowsable, ICustomFunctionOperatorFormattable, _
    ICustomCriteriaOperatorQueryable
    Private Const FunctionName As String = "MyConcat"
    ' ...

    Public Function GetCriteria(ParamArray ByVal operands() As CriteriaOperator) As CriteriaOperator
        If operands Is Nothing OrElse operands.Length <> 1 OrElse _
        Not(TypeOf operands(0) Is MemberInitOperator) Then
            Throw New ArgumentException(FunctionName)
        End If
        Dim operandCollection As New CriteriaOperatorCollection()
        For Each operand As XPMemberAssignment In (CType(operands(0), MemberInitOperator)).Members
            operandCollection.Add(operand.Property)
        Next operand
        Return New FunctionOperator(FunctionName, operandCollection)
    End Function
End Class