generic-constraints – Tarik Billa

What exactly is a “Special Class”?

December 25, 2022 by Tarik

From the Roslyn source code, it looks like a list of hardcoded types in isValidConstraintType: switch (type.SpecialType) { case SpecialType.System_Object: case SpecialType.System_ValueType: case SpecialType.System_Enum: case SpecialType.System_Delegate: case SpecialType.System_MulticastDelegate: case SpecialType.System_Array: // “Constraint cannot be special class ‘{0}'” Error(diagnostics, ErrorCode.ERR_SpecialTypeAsBound, syntax, type); return false; } isValidConstraintType in GitHub (updated with new types) IsValidConstraintType is Roslyn Source … Read more

Is there a generic constructor with parameter constraint in C#?

October 19, 2022 by Tarik

As you’ve found, you can’t do this. As a workaround I normally supply a delegate that can create objects of type T: public class A { public static void Method<T> (T a, Func<float[,], T> creator) { //…do something… } }

Create Generic method constraining T to an Enum

August 29, 2022 by Tarik

Since Enum Type implements IConvertible interface, a better implementation should be something like this: public T GetEnumFromString<T>(string value) where T : struct, IConvertible { if (!typeof(T).IsEnum) { throw new ArgumentException(“T must be an enumerated type”); } //… } This will still permit passing of value types implementing IConvertible. The chances are rare though.