Struct initialization and new operator

Question

I have two similar structs in C#, each one holds an integer, but the latter has get/set accessors implemented.

Why do I have to initialize the Y struct with

Answer 1

In first case you just assigning field. It doesn't involve actual using of structure, just setting value into memory (struct address + field offset on stack).

In second case you calling method set_a(int value), but fail because variable is uninitialized.

In third case constructor initializes it for you, so using variable is ok.

Update: Here comes the specification!

"12.3 Definite assignment" (page 122 of ecma-334).

A struct-type variable is considered definitely assigned if each of its instance variables is considered definitely assigned