C# void type- safety

Question

I am just new for C# programming (coming from C++)

My question is: In C# every type inherits from Object Why \'void\' doesn`t?Can it cause some RT/type safety problems

Answer 1

Unlike C++, C# allows the void keyword only to specify that a method does not have a return type.

In C#, the void keyword is invalid as a method parameter. In C++, however, void can be used to specify a "universal" pointer.

One caveat to this rule is when using unsafe code, which is generally unnecessary in C#.

EDIT: Contrary to what some others have posted, there's a difference between void and System.Void. There is a void keyword, in addition to the struct System.Void. The keyword is used to indicate that a method does not have a return type. System.Void, on the other hand, is used in reflection to ask which type a method returns (there may be other uses for System.Void, but I'm not aware of any).

C# void keyword
C++ void keyword

Answer 2

Void is a Type, but methods that return void, don't push anything onto the stack. System.Void is declared as a struct, so it should inherit from object, too, but it's handled differently. You can see it clearer if you look at the IL code, after a method returning void is called, there is no pop instruction, which normally is used to pop unused return values off the stack.

EDIT: Actually, i checked. If i declare a method as returning System.Void, i get an error message stating that System.Void can't be used from C# code. But try the following:

typeof(object).IsAssignableFrom(typeof(void))
typeof(System.ValueType).IsAssignableFrom(typeof(void))

that will return true, so void does derive from object and System.ValueType (i.e. struct)

Answer 3

Void is not a type of object. It's a type of nothing. At least in C#, just about the only time you use the word void is as a function return type, so it means the function returns nothing. Non-existence of something can't derive from anything. The only other place to use it is in unsafe context, referring to pointers, which also do not derive from Object.

Answer 4

In C#, void is a keyword that is used in two contexts:

• In the context of method signatures, void indicates the absence of a return type; it doesn't refer to a type "void" which could inherit from object.

  (In reflection, a return type has always to be specified. For this reason, there is a System.Void type in the framework, but void and System.Void cannot be used interchangeably.)

• In unsafe context, void* is a pointer type to an unknown type. As mentioned in the blog post linked by @Colin Mackay, pointer types do not inherit from object, although they can be converted to one.

Answer 5

Not everything inherits from Object - That is a common myth. Interfaces don't inherit from Object.

See this for more details: http://blogs.msdn.com/ericlippert/archive/2009/08/06/not-everything-derives-from-object.aspx