Make Option<T>.ToString return string value of Some or blank

[Atif Aziz]

Option<T>.ToString() is currently implemented to return a string representation of Option<T>'s state when ideally it should simply return a blank when None or Some(null) and the string representation of the value of Some otherwise. In other words:

        public override string ToString() =>
            hasValue && value != null ? value.ToString() : string.Empty;

Doing so will go a long way to help Option<T> to be easily substituted in code for Nullable<T> and references where one desires. The trouble with the current implementation is that any refactoring towards Option<T> will require one to thoroughly review all code where string formatting is used. For example, suppose the following code:

var d = (DateTime?) new DateTime(2010, 12, 31)
var s = string.Format(new CultureInfo("de-DE"), "{0:D}", d);
Console.WriteLine(s);

This prints:

Freitag, 31. Dezember 2010

However, if you use Option<T> instead:

var d = Option.Some(new DateTime(2010, 12, 31));
var s = string.Format(new CultureInfo("de-DE"), "{0:D}", d);
Console.WriteLine(s);

then output changes to (depending on the thread's default culture) something along the lines of:

Some(31/12/2010 00:00:00)

If you have unit tests then you can catch this sort of issue otherwise your luck will be your friend or your enemy. Either way, the fix looks ugly:

var d = Option.Some(new DateTime(2010, 12, 31));
var s = string.Format(new CultureInfo("de-DE"), "{0:D}",
                      d.Match(v => v, () => default(DateTime?)));
Console.WriteLine(s);

For debugging purposes, one can still rely on DebuggerDisplayAttribute to display the string representation as it is today.

[Nils Lück]

Hi,

I think consistency with nullable is a good idea, and a very reasonable expectation (in retrospect, it seems like the obvious thing to do).

I consider the suggestion approved. It is, however, a breaking change, so I will designate this for version 4.0.0.

Thanks a lot for the input!

[mathiasbaert]

Hi @nlkl
I'm wondering why this change was removed again from 4.0.0
Do you no longer consider this to be the preferred behavior
or were there unforeseen problems?