Default parameter for value must be a compile time constant?

Question

This is my method signature. While trying to pass end as an optional parameter it gives me this error. What should I do to resolve this? Why isn't DateTime.MinValue a constant?

public static void DatesToPeriodConverter(DateTime start, DateTime end = DateTime.MinValue,                                           out string date, out string time) 

Answer 1

DateTime.MinValue is not a const, because the language doesn't like const on DateTime. One option is to use DateTime? instead, i.e.

public static void DatesToPeriodConverter(DateTime start, DateTime? end = null,      out string date, out string time) {     var effectiveEnd = end ?? DateTime.MinValue;     // ... } 

However, you will still have the issue of having non-default parameters after default parameters - you may need to re-order them to use that as a default.

Answer 2

Use regular method overloads instead:

public static void DatesToPeriodConverter(DateTime start, out string date, out string time) {     DatesToPeriodConverter(start, DateTime.MinValue, out date, out time);   }  public static void DatesToPeriodConverter(DateTime start, DateTime end, out string date, out string time)  { } 

Atlernatively, default(DateTime) is the same as DateTime.MinValue and is compile time constant, but I tend to err away from using this style (there's no guarantee in future that default(DateTime) will equal DateTime.MinValue):

public static void DatesToPeriodConverter(DateTime start, DateTime end = default(DateTime), out string date, out string time) 

Or as Marc suggests, use DateTime? which allows a null default value.