Did you know that you can assign any integral type value to an enum even if it is not part of the enum values?

Consider the following int based enum.

public enum FunRunDistances
    FiveKilometers = 5,
    TenKilometers = 10,
    HalfMarathon = 21,
    Marathon = 42

Although 5, 10, 21 and 42 have been explicitly added as values of the FunRunDistances enum, the following code does not produce an error:

FunRunDistances funRun = (FunRunDistances)100;

Clearly you should not do this in your code as most developers will expect all enum based variables to bet set from a value that is defined in the enum. This is all good and well, except sometimes you aren’t the in control of how the value of enum is set. For instance a Web API, or reading from a database value, etc.

Enter Enum.IsDefined(Type, Object) Method

As per the .NET docs, this method:

Returns an indication whether a constant with a specified value exists in a specified enumeration.

So we can use this method to determine whether the enum value falls within the defined values of the FunRunDistances enum:

var isDefined = Enum.IsDefined(typeof(FunRunDistances), funRun);
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