Do all C# casts result in boxing/unboxing

Question

I am curious to know if all casts in C# result in boxing, and if not, are all casts a costly operation?

Example taken from Boxing and Unboxing (C# Programming Guide)

Answer 1

I am curious to know if all casts in C# result in boxing,

No. Boxing is a very special operation that means treating an instance of a value type as an instance of a reference type. For reference type conversion to reference type conversion, the concept plays no role.

are all casts a costly operation?

Short answer: No.

Long answer: Define costly. Still no, though.

What about casts from 2 different types of reference types? what is the cost of that?

Well, what if it's just a derived to base reference conversion? That's BLAZINGLY fast because nothing happens.

Other, user-defined conversions, could be "slow", they could be "fast."

This one is "slow."

class A { public int Foo { get; set; } }
class B {
    public int Foo { get; set; }
    static Random rg = new Random();
    static explicit operator A(B b) {
        Thread.Sleep(rg.Next());
        return new A { Foo = b.Foo; }
    }
}

This one is "fast."

class A { public int Foo { get; set; } }
class B {
    public int Foo { get; set; }
    static Random rg = new Random();
    static explicit operator A(B b) {
        return new A { Foo = b.Foo; }
    }
}

var obj2 = (A)obj; // is this an "expensive" operation? this is not boxing

No, it's "cheap."