Thread: why can't a constant field be of non-built-in struct type?

Code:

class T
{
        enum E { }
        struct S { }
        interface I { }
        delegate void D();
        class C { }

        const E e = new E();
        //const S s = default(S);
        const I i = default(I);
        const D d = default(D);
        const C c = default(C);

        const int x = 10;
        const string y = "s";

}

All of the above are possible except the constant field of a type that is a struct. I can see why the non-string reference types would default to the only literal expression they can represent - null - and if I'm not mistaken the default value of a struct is an instance of the struct with all its fields set to their default value, but why is it that a const struct field is not possible? is there a reason why or is it just the way c# was written? oh and by the way, what's the idea of allowing enum types to have a default constructor?

Originally Posted by VirtualAce

To clarify, a C# struct cannot have an explicit parameterless constructor b/c compilers do not generate default constructors for value types. So even if the compiler allowed you to provide one it would never be called which would make the constructor useless.

I know that C# structs can't have explicit parameterless instance constructors but your explanation doesn't help me understand why that's the case. You say that even if the compiler allowed you to provide one it would never be called. Do you mean to say that even if I could get around the pre-compile restrictions and throw one in the compiler still wouldn't generate IL code for that constructor? can you elaborate a bit more and maybe explain why compilers won't generate default constructors for value types? is it because that's the way it is or is there a reason why that's the case?

I did not design the language so I do not understand the reasoning behind it. If you want more information I would purchase a book on C# or perhaps do some research on MSDN to find out why this is. What I posted is how it behaves and not the why.