关于内存操作员的C＃内存分配

Question

I've been running benchmark tests trying to determine the best way of handling many vector operations. I'm not worried about computational efficiency, but memory allocation so that my program doesn't get a big hit from the garbage collector cleaning up excess vectors in the heap. The standard vector operations (+, *, normalize) are static operator overloads that take in two vectors and returns a new vector. Since these use the new operator, I thought that it would allocate memory in the heap and set the assigning variable to that memory location. This got to my initial hypothesis of using methods that would update an existing vector if that vector was the assigning variable.

This is the standard code that uses Vector operations.

var object1Pos = new Vector2(10, 5);
var object2Pos = new Vector2(-5, 3);
Vector2 object1Trajectory = (object2Pos - object1Pos).normalized;
object1Trajectory *= 8;
object1Pos += object1Trajectory;

This is the code that uses methods to update a vector.

var object1Pos = new Vector2(10, 5);
var object2Pos = new Vector2(-5, 3);
var object1Trajectory = new Vector2(object2Pos);
object1Trajectory.Add(object1Pos * -1);
object1Trajectory.Normalize();
object1Trajectory.Scale(8);
object1Pos.Add(object1Trajectory);

Running the benchmark test, while the method code is 35% more efficient than the operator code (though the increase isn't that significant) the amount allocated to the heap and cleaned by the garbage collector was the same. This doesn't make sense to me, since this shows that either the vectors generated by the operators are generated on the stack, or they compiler is doing some optimizations so it doesn't have to allocate new memory in the heap. I would like to know how c# allocates memory and what the compiler does so that extra memory isn't allocated that will only be used in the method?

Answer 1

The new operator doesn't mean heap allocation in C#. Vector2 is most likely a struct, so as long as it is a local variable and you're not doing something special like capturing it in a lambda it will be allocated on the stack even when you use new .

For additional information on types and associated storage, please see Eric Lippert's great post on the subject.