Does every type in .net inherit from System.Object? [duplicate]

Answer 1

As far as your question is concerned, structs inherit from ValueType implicitly, which in turn derives from object.

Other than that, Eric Lippert's link posted above is what you would like to read.

Answer 2

Just few weeks ago Eric Lippert blogged about this: Not everything derives from object. A great read.

Answer 3

Not every type, but System.Double does.

From Eric Lippert's post:

All value types, including enums and nullable types, derive from object

In C# struct is syntatic sugar for System.ValueType, meaning that System.Double derives from System.ValueType. Since System.ValueType derives from System.Object, System.Double does too. You can see that using the .Net Framework source code or using .Net Reflector:

.class public sequential ansi serializable sealed beforefieldinit Double
    extends System.ValueType

UPDATE:

On the toolbar, if you select C#, you'll see (This is what you are seeing): alt text http://bqqqkg.bay.livefilestore.com/y1pk3EAm_SJtl4dn51HLrhdgHAXCS08-xY9nQUARCpT4WnBQyRHD4RLmIK9zZ4okJXMj7Xopg1EBuY_Od7_oWz7Pw/DoubleCSharp.jpg

If you change the ComboBox and select IL then you'll see: alt text http://bqqqkg.bay.livefilestore.com/y1pRXk-0rDvFjj7b8EqU9-bydzpWjVGJMq8pDbiCr6aALob3j-aC9vvbeBS4vQRedHJ5Dh2CWtYRCywMJ9FGHOaaw/DoubleIL.jpg

See that in IL, Double extends System.ValueType

Answer 4

Eric Lippert has covered this in a blog entry: Not everything derives from object (This is the title of the blog entry; not the answer to this question. Don't get confused.)

Yes, all structs inherit from System.ValueType which in turn inherits from System.Object. enums you declare inherit from System.Enum which inherits from System.ValueType.

Update:

Inherently, there's not a problem with a value type being derived from a reference type. Inheritance is a "is-a" relationship between two types. However, in order to treat a value type as an object instance, it has to be boxed. This is done implicitly when you are passing a value to a method that expects an object parameter (or when you call instance methods implemented in System.Object.)