Equivalent to Java's Optional.orElse in C#

Question

I'm looking for nice syntax for providing a default value in the case of null. I've been used to using Optional's instead of null in Java where API's are concerned, and was wondering if C#'s nicer nullable types have an equivalent?

Optionals

Optional<String> x = Optional<String>.absent();
String y = x.orElse("NeedToCheckforNull"); //y = NeedToCheckforNull

@nullable

String x = null;
String y = x == null ? "NeedToCheckforNull" : x ; //y = NeedToCheckforNull

How would I make the above more readable in C#?

JavaScript would allow y = x | "NeedToCheckforNull"

Side note: string is not "nullable type" ... It is just regular reference type, nullable type would be `int?`. — Alexei Levenkov, Sep 01 '17 at 04:07

score 11 · Accepted Answer · edited Aug 08 '20 at 21:00

11

You can use the ?? operator.

Your code will be updated to:

string x = null;
string y = x ?? "NeedToCheckforNull";

See: ?? Operator (C# Reference)

edited Aug 08 '20 at 21:00

Peter Mortensen

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answered Sep 01 '17 at 04:05

d.moncada

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score 4 · Answer 2 · edited Jun 15 '21 at 11:31

4

C# has the special Nullable<T> type which can be declared with int?, decimal?, etc. These can provide a default value by using .GetValueOrDefault(), T GetValueOrDefault(T defaultValue), and the ?? operator.

string x = null;
Console.WriteLine(x ?? "NeedToCheckforNull");

edited Jun 15 '21 at 11:31

granadaCoder

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answered Sep 25 '17 at 10:08

steven7sheng

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score 0 · Answer 3 · answered Jan 27 '20 at 07:56

0

I've created my own.

public class Optional<T> {
    private T value;
    public bool IsPresent { get; private set; } = false;

    private Optional() { }

    public static Optional<T> Empty() {
        return new Optional<T>();
    }

    public static Optional<T> Of(T value) {
        Optional<T> obj = new Optional<T>();
        obj.Set(value);
        return obj;
    }

    public void Set(T value) {
        this.value = value;
        IsPresent = true;
    }

    public T Get() {
        return value;
    }
}

answered Jan 27 '20 at 07:56

SM Adnan

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may I suggest you use a struct to provide that instead of a class – jalsh Jul 26 '20 at 15:26
As it is mutable, I prefer using class. – SM Adnan Jul 27 '20 at 11:07
Another reason of not using struct is it can contain data of larger than 16 bytes. Reference: https://docs.microsoft.com/en-us/dotnet/standard/design-guidelines/choosing-between-class-and-struct – SM Adnan Jul 27 '20 at 11:07
2

Optional should be immutable, the doc you're referencing discourages the use of struct when it has *all* the mentioned characteristics, so the fact that it's not larger than 16 bytes doesn't change it. Optional should be a sturct, just like Nullable is – jalsh Sep 18 '20 at 03:46

score 0 · Answer 4 · answered Oct 13 '20 at 15:34

0

consider using language extensions option type

int x = optional.IfNone("NeedToCheckforNull");

answered Oct 13 '20 at 15:34

Elazar Neeman

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Equivalent to Java's Optional.orElse in C#

4 Answers4