How to Create a TypeScript like String Literal Union type in C#

Question

I’m working in C# with some JSON & an API. I'm wondering how to handle something like this.

One of the JSON values is a string that can be one of the following values: “Last_Day”, “Last_Week”, “Last_Month”.

In TypeScript I can do this:

type DateSince = "Last_Day" | "Last_Week" | "Last_Month"

Then I get type hinting like this:

If the value is anything but those 3 strings, I get the red squiggle line error. My value is still technically a string as well, which is what I need to use with the JSON API requests and responses.

I have yet to find a great way to do this in C#. Is it even possible to do this in C# with relative ease?

My ideal solution lets me assign a custom type to a variable instead of using a string. This way I don't have to remember the possible string values.

Whether or not this is literally an enumerated type is irrelevant. You have an enumeration of strings as a de facto enum, so it still applies. — Patrick Roberts
– Patrick Roberts, Commented Jun 29, 2018 at 15:57

2 revs · Accepted Answer · 2018-06-29 16:36:37Z

6

As suggested by @PatrickRoberts & @afrazier, the best way is using enums and the Json.NET StringEnumConverter.

[JsonConverter(typeof(StringEnumConverter))]
public enum DateSince
{
    [EnumMember(Value = "LAST_DAY")]
    LastDay,
    [EnumMember(Value = "LAST_WEEK")]
    LastWeek,
    [EnumMember(Value = "LAST_MONTH")]
    LastMonth,
}

Customizing Enumeration Member Values

edited Jun 29, 2018 at 16:36

community wiki

2 revs
mattferderer

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Comments

vendettamit · Accepted Answer · 2018-06-29 15:42:59Z

3

In C# you can use Enums.

public enum DateSince
{
    Last_Day ,
    Last_Week,
    Last_Month
}

Usage:

var datesince = DateSince.Last_Day;

9 Comments

Patrick Roberts Over a year ago

While I generally agree with this answer, it doesn't really address this particular point without more research on the asker's part: My value is still technically a string as well, which is what I need to use with the JSON API requests and responses. Unless you were FGITW'ing and were going to add that in an edit...

Patrick Roberts Over a year ago

@mattferderer you should still use enums, just use JSON.net for serialization / parsing and provide this property attribute to your enum values.

afrazier Over a year ago

JSON.NET can take care of serializing and deserializing the enum with StringEnumConverter.

vendettamit Over a year ago

Then you should go with @afrazier 's suggestion. Use enum converter for JSON serialization.

Patrick Roberts Over a year ago

If you weren't using JSON and serialization, why would you still care about its string value? Refactor the rest of your code to expect an enum, it's better practice in C#.

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