What is the syntax to assign multiple enum values to a property in F#?

Question

I am writing a ServiceStack webservice in F# and need to limit some of the features (removing SOAP support for instance).

In C# I am using the pipe operation to assign multiple Enums (ServiceStack.ServiceHost.Feature) to the EnableFeatures property like so:

SetConfig(new EndpointHostConfig
{
    DebugMode = true, //Show StackTraces in responses in development
    EnableFeatures = Feature.Json | Feature.Xml | Feature.Html | Feature.Metadata | Feature.Jsv
});

However in F# you can't use pipe to accomplish this, and everything else I try is attempting to do function application to the enums. How do I go about assigning multiple enums in this case?

You've already got an answer, but it's worth noting this is not a pipe operator, it's 'bitwise or'. F#'s bitwise or operator, as pointed out by Craig Stuntz, is `|||`. — Matthew Walton, May 18 '12 at 15:56
@botanist Good to see you here--there are some really smart F# folks hereabouts. And there's me too. — Onorio Catenacci, May 18 '12 at 16:28
@Daniel For your convenience: `let inline (|||||||) a b = a ||| b` :-) — Tomas Petricek, May 18 '12 at 17:04
@TomasPetricek: :-) Thanks. Is it possible to get something like this to work: `let inline flags<'T, 'U when 'T : enum<'U>> items = List.reduce (|||) items`? — Daniel, May 18 '12 at 17:06

Craig Stuntz · Accepted Answer · 2012-05-18T16:34:12.780

22

Use a triple pipe:

EnableFeatures = Feature.Json ||| Feature.Xml ||| Feature.Html ||| Feature.Metadata ||| Feature.Jsv

edited May 18 '12 at 16:34

answered May 18 '12 at 15:44

Craig Stuntz

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Thank you sir! I figured I was missing something simple, and indeed I was. [F# Bitwise Operators](http://msdn.microsoft.com/en-us/library/dd469495.aspx) – John B Fair May 18 '12 at 17:00

score 13 · Answer 2 · answered May 18 '12 at 16:04

13

If you have a bunch of them you can save a few keystrokes with reduce:

List.reduce (|||) [Feature.Json; Feature.Xml; Feature.Html; Feature.Metadata]

answered May 18 '12 at 16:04

Daniel

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score 0 · Answer 3 · answered May 18 '12 at 15:43

0

You would create the value based on the construction of the underlying values:

EnabledFeatures = enum<Feature>(16); // or whatever the full flag value would be for Json + Xml + Html + Metadata, etc

answered May 18 '12 at 15:43

Tejs

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7

You could, but that's why we have symbolic names for flags and bitwise combining operators in the first place - so we don't have to. – Matthew Walton May 18 '12 at 15:57

What is the syntax to assign multiple enum values to a property in F#?

3 Answers3