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) 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.
DateTime? means Nullable<DateTime>, meaning "a value that can either be a DateTime or null"; the ?? is the null-coalescing operator, which means (in this context): take the first non-null value, i.e. take end if it is non-null, otherwise DateTime.MinValue
end ??= DateTime.MinValue;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.
=default(DateTime) works here, when const DateTime x = default(DateTime); does not.const int MyInt = default(int) works fine, the compiler first complains that DateTime is not actually a valid const.
=null works for references, even though you can't declare a reference as const. Supporting const for datatypes which have exactly one valid const strikes me as somewhat unnecessary. On the other hand, supporting =null for default arguments is obviously useful.
class Foo { public Foo(List<string> items = new List<string>()) { } }. Changing new List<string>() to default(List<string>) solved the problem for meChange a type of the parameter end to a Nullable and use null as a default value:
public static void DatesToPeriodConverter(DateTime start, DateTime? end = null, out string date, out string time) or use default(DateTime) as a default value:
public static void DatesToPeriodConverter(DateTime start, DateTime end = default(DateTime), out string date, out string time) You can try doing it this way:
public static void DatesToPeriodConverter(DateTime start, DateTime? end , out string date, out string time) { if(!end.HasValue){ end = DateTime.MinValue; } } You are correct. Default parameter for value must be a compile time constant. Dynamically calculated value is not accepted by compiler against optional parameter. The reason behind this may be that it is not definite that the dynamic value you are providing would give some valid value.
Optional parameters must appear at the end of the parameter list. out parameters must also appear at the end of the parameter list. Your optional parameter is not an out parameter.
Furthermore, you can't use default values for optional parameters other than literal constants and a few weird corner cases.
All facts point in the following direction:
This error can happen with Lists as well:
CS1736 Default parameter value for 'dateTimes' must be a compile-time constant
public YourEntity(dateTimes = new List<DateTime>()) { DateTimes = dateTimes; } public List<DateTime> DateTimes { get; set; } = new List<DateTime>(); You can solve it like this then:
public YourEntity(dateTimes = null) { DateTimes = dateTimes != null ? dateTimes : new List<DateTime>(); } public List<DateTime> DateTimes { get; set; } = new List<DateTime>(); we can create CONSTANTS class with default values
public const int DEFAULTINT = -9999;
and use them as CONSTANTS.DEFAULTINT as business defaults..
hope it helps,
DateTime.