private bool IsValidUserDefinedOperatorSignature(int parameterCount) =>
!this.ReturnsVoid &&
!this.IsGenericMethod &&
!this.IsVararg &&
this.Parameters.Length == parameterCount &&
this.Parameters.All(p => p.RefKind == RefKind.None) && //this.ParameterRefKinds.IsDefault && // No 'ref' or 'out'
!this.IsParams();