Why can't I initialize my fields in my structs?

Question

I am surprised that I can't initialize my fields in structs, why is it like that? Like:

struct MyStruct
{
    private int a = 90;
}

but it's a complie time error. I don't know why it's a problem? Please explain this to me.

Answer 1

In C#, a struct cannot declare a default constructor.

The compiler moves the initialization statements to the constructor, which can't happen with a struct in C#.

Answer 2

The reason is mainly performance. Consider the following,

var a = new MyStruct[1000];

If C# allowed initialization of fields in a struct then the initialization would have to be performed 1000 times, once for each element in the array. C# wanted to avoid such kinds of implicit behavior as might be found in other languages.

Answer 3

That's because your assignment is actually transformed by the compiler to be done in the default constructor. But C# structs don't have default constructors, as you can see in the link posted by Kent Boogaart.

Answer 4

It's for performance. When you new up a struct with the default constructor, all it does is allocate however many bytes on the stack and initialises them to 0.