C＃对象初始化

Question

Having program with such code :

var subtree = new Tree<int>(5, EnumeratorOrder.BreadthFirstSearch) { 1, 2 };

var tree = new Tree<int>(7, EnumeratorOrder.BreadthFirstSearch) { subtree, 10, 15 };

I сan't understan what means { 1, 2 } ?

Answer 1

I сan't understan what means { 1, 2 }

The {1, 2} are Collection Initializers .

They represent a short-hand version of

var temp = new Tree<int>(5, EnumeratorOrder.BreadthFirstSearch);
temp.Add(1);
temp.Add(2);

var subtree = temp;

Note regarding initial assignment to temp : The meaning of assignment is evaluate the left, evaluate the right, do the assignment. Evaluating the right produces side effects, and those effects must be ordered before the effect of the assignment. See comments for a full discussion.

Answer 2

It's a collection initializer .

Collection initializers let you specify one or more element initializers when you initialize a collection class that implements IEnumerable or a class with an Add extension method. The element initializers can be a simple value, an expression or an object initializer. By using a collection initializer you do not have to specify multiple calls to the Add method of the class in your source code; the compiler adds the calls.