Object type comparison

[egorvts]

Recently bumped into an interesting problem (?) with object comparison:

• When I compare types like that, it works as expected: obj?.GetType() == typeof(ReadonlyBytes)
• But when I use obj is ReadOnlyBytes, it returns True comparing to instance of any derived class

Is this an issue or a design decision?

[FaustVX]

Yes it's the how it's designed

• obj is ReadOnlyBytes can be seen as if obj can be assigned to a variable of type ReadOnlyBytes
  • you can also use pattern matching: if (obj is ReadOnlyBytes bytes) { /* use bytes here */ }
• obj?.GetType() == typeof(ReadonlyBytes) check if obj is exactly ReadonlyBytes
  • it's not the recommended way

[TahirAhmadov]

See also typeof(ReadOnlyBytes).IsAssignableFrom(obj.GetType())

[HaloFour]

From the documentation: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/type-testing-and-cast#is-operator

The is operator checks if the run-time type of an expression result is compatible with a given type.

It also lists all of the cases in which the operands are considered compatible.