Type Overflow...

[Bernhard Hiller]

I have an interface and a type implementing it:

public interface IValueWithUnit {...}
[Serializable]
public struct DoubleValueWithUnit : IValueWithUnit { ... }

At a different place, I have a string with the name of the type, and must find out if the type derives from above interface:

string name = "DoubleValueWithUnit";
Type t;
if (TypeHelper.TryFindType(name, out t))
{
m_IsValueWithUnit = t.IsSubclassOf(typeof(IValueWithUnit)); // false
m_IsValueWithUnit = t.IsSubclassOf(typeof(DoubleValueWithUnit)); // false
m_IsValueWithUnit = t.IsInstanceOfType(typeof(IValueWithUnit)); // false
m_IsValueWithUnit = t.IsInstanceOfType(typeof(DoubleValueWithUnit)); // false
m_IsValueWithUnit = t.IsAssignableFrom(typeof(IValueWithUnit)); // false
m_IsValueWithUnit = t.IsAssignableFrom(typeof(DoubleValueWithUnit)); // true
m_IsValueWithUnit = t.GetInterface(nameof(IValueWithUnit)) != null; // true

The TryFindType function is from c# - Type.GetType("namespace.a.b.ClassName") returns null - Stack Overflow[^]. You see the many "false" comments? DoubleValueWithUnit is neither a subclass nor an instance of DoubleValueWithUnit or IValueWithUnit, and is also not assignable from IValueWithUnit, but at least it is assignable from DoubleValueWithUnit. I am confused now: my brain threw a TypeOverflowException.

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!

[phil o]

What is the relation between the name variable, and the m_Setting.Type property? Here's what I can understand from the results you get:

• DoubleValueWithUnit is not a subclass of IValueWithUnit. An interface implementation is not considered as inheritance.
• DoubleValueWithUnit is not a subclass of DoubleValueWithUnit. It is the very same class.
• DoubleValueWithUnit is not an instance of IValueWithUnit. It is the type itself, not an instance of the type.
• DoubleValueWithUnit is not an instance of DoubleValueWithUnit. Same comment as above.
• DoubleValueWithUnit is not assignable from IValueWithUnit. It implements the interface, but that does not mean that every implementation of the interface should allow to cast to actual type. There could be some properties/methods of the class which are not part of the interface.
• DoubleValueWithUnit is assignable from DoubleValueWithUnit. This one seems logical.
• DoubleValueWithUnit implements IValueWithUnit. Thus IValueWithUnit is an element of the list of interfaces implemented by DoubleValueWithUnit.

"Five fruits and vegetables a day? What a joke! Personally, after the third watermelon, I'm full."

[Bernhard Hiller]

phil.o wrote:

What is the relation between the name variable, and the m_Setting.Type property?

Oh, I forgot to replace that; question updated. Thanks for your explanation!

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!

[Richard Deeming]

As Phil explained, you've got the IsAssignableFrom the wrong way round:

m_IsValueWithUnit = typeof(IValueWithUnit).IsAssignableFrom(t); // true

But rest assured you're not alone in being confused by that method. :) Nick Craver on Twitter: "Anyone else pretty reliably get .IsAssignableFrom() backwards?"[^]

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[Bernhard Hiller]

Thanks. Good to know that.

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!