How to pass generic type as parameter to Enum.Parse()

Question

I have a class with a generic method:

public record OperationCollectionGeneric<OPERATIONTYPE> where OPERATIONTYPE: notnull, Enum { public OPERATIONTYPE Group { get; } public OperationCollectionGeneric(string part1, string? part2 = null, string? part3 = null) { Group = Enum.Parse<OPERATIONTYPE>(part1, true); }

The Enum.Parse() method has the following error:

Error CS0453 The type 'OPERATIONTYPE' must be a non-nullable value type in order to use it as parameter 'TEnum' in the generic type or method 'Enum.Parse(ReadOnlySpan, bool)'

How can I pass the make sure that OPERATIONTYPE parameter is of type Enum

I tried to use the where keywork to set the enum type for the OPERATIONTYPE but it does not work.

You need where OPERATIONTYPE: struct, Enum. The constraint you have lets someone do OperationCollectionGeneric<Enum>, where you literally pass the Enum type — canton7
– canton7, Commented Nov 28, 2022 at 13:56
"must be a non-nullable value type". You probably fixated on the "not-nullable" bit, but the important part was "value type"; struct defines a value type. — Connor Low
– Connor Low, Commented Nov 28, 2022 at 15:00

Guru Stron · Accepted Answer · 2022-11-28 13:55:54Z

Enum.Parse is restricted to struct's, so change generic constraints to match it:

public record OperationCollectionGeneric<OPERATIONTYPE> where OPERATIONTYPE : struct, Enum

Roman Ryzhiy · Accepted Answer · 2022-11-28 13:56:25Z

-1

OPERATIONTYPE must be a non-nullable value type, but System.Enum is a reference type.

answered Nov 28, 2022 at 13:56

Roman Ryzhiy

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1 Comment

Guru Stron Over a year ago

System.Enum is a very special type which inherits from another very special type System.ValueType - base class for every value type.

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