How do I print an Instant as rfc2822 in NodaTime?

I'd prefer a built-in named pattern over supplying all formatting to ToString.

If you mean you're expecting a "standard" pattern so to speak, there isn't one.

However, it's easy enough to write a custom pattern for this - giving you an InstantPattern instead of passing it all in ToString, as you mentioned.

Fortunately, formatting RFC 2822 is considerably simpler than parsing it - especially if you're happy to express everything in UTC. Looking at RFC 2822 itself, two things spring out:

• "The date and time-of-day SHOULD express local time." If you want to go along with that, you should be formatting an OffsetDateTime instead of an Instant.

• The day-of-week is optional - but in my experience it's pretty much expected to be there.

Ignoring the "should express local time" part, I'd use:

var pattern = InstantPattern.CreateWithInvariantCulture
   ("ddd d MMM yyyy HH:mm:ss '+0000'");
// Test it...
Console.WriteLine(pattern.Format(SystemClock.Instance.Now));

(Note for future readers: as of Noda Time 2.0, use IClock.GetCurrentInstant() instead of IClock.Now.)

Sample output:

Sat 4 Apr 2015 09:55:49 +0000

If you want to go down the OffsetDateTimePattern route, you want:

var pattern = OffsetDateTimePattern.CreateWithInvariantCulture
    ("ddd d MMM yyyy HH:mm:ss o<+HHmm>");

Then you'll get output such as:

Sat 4 Apr 2015 10:57:27 +0100