C# supports value types and reference types, but are they all objects?

Question

I know C# has both value and reference types, but how can you do a this:

int age = 100;

string blah = age.ToString();

If age is a value type, how does it have a ToString method on it? Does it get converted to an object ONLY when required internally then?

Answer 1

If age is a value type, how does it have a ToString method on it?

Value types are allowed to have methods on them. Why wouldn't they? A method "on a type" is just a hunk of code that happens to be associated with a particular type; why do you believe that it matters whether that type is classified as a "reference type" or "value type"?

That's not a rhetorical question. I am interested in learning about what intuitions people have about code, particularly when those intuitions are incorrect. By understanding what people get wrong intuitively, we can try to come up with better abstractions that are more intuitive.

Does it get converted to an object ONLY when required internally then?

What exactly do you mean by "converted to an object"? Do you mean "boxed"?

There are many situations in which a value type must be boxed. Some of them are straightforward -- like when you cast a value type to object or an interface. Some of them are obscure. (There are bizarre situations in generic methods where we must box and unbox things in ways you might not expect.)

In this particular situation there is no boxing. Calling a method directly implemented on a value type simply calls that hunk of code. There's no need to treat the thing as "object"; the hunk of code we're calling knows the type of the thing.

Answer 2

You want to look up boxing/unboxing.

Boxing

Answer 3

System.Int32 inherits System.ValueType which inherits System.Object.

All class, struct, enum, array, nullable and delegate types eventually derive from object. All interface types and type parameter types are implicitly convertible to object. And all pointer types neither derive from nor are convertible to object