Is it okay to use "a = new type(...);" where type is a small struct in routines

Question

I've been thinking on how the memory would be handled in some specific case which i'll explain (C# 4.0).

To begin with, i've read Eric Lippert answer in order to know what will be invoked whenever I use new on a variable of type struct

And now, I wonder if the compiler "produces" intelligent code in specific use of the new keyword

To be precise, what will it do if the new is set on a return instruction or even on operator = ?

Assume we have a struct Coord defined as follow:

struct Coord {
    int x, y;
    public Coord(int xx, int yy) {
        x = xx;
        y = yy;
    }
}

I'll use this struct to store position and velocity in classes (suppose we call them Entity) that have geometric behaviors

Entity is defined as follow:

class Entity {
    private Coord m_pos, m_vel;
    //...
    public Entity() {
        // ...
    }

    public Coord Position {
        get {
            return m_pos;
        }
        set {
            m_pos = value;
        }
    }

    public Coord Velocity {
        get {
            return m_vel;
        }
        set {
            m_vel = value;
        }
    }
}

My main program contains a routine which simply update my entities (and so their position and velocity as well)

Now my question is : What's the price, if I decide to update these 2 members by using new on it:

Entity a; // initialized

...

private Coord getNewPosOf(Entity e) {
   ...
   return new Coord(computed_x, computed_y);
}

public void routine() {
    a.Velocity = new Coord(x_vel, y_vel);
    a.Position = getNewPosOf(a);
}

Will that code allocate memory in the short-term storage and therefore also copy values from the constructor to the memory location of a. Or will the compiler take care of things and avoid allocating and copying memory in that specific case?

Note: I have the feeling i'm doings things wrong, maybe I should not be using Properties to edit my Coord-type members (or worst, I may not use Properties correctly and there is another way to do what I want)

Do you have a performance problem? – Jodrell Mar 27 '12 at 11:24 — Jodrell, Mar 27 '12 at 11:24
Not yet, but I would like to be sure of what i'm doing. – Salepate Mar 27 '12 at 11:27 — Salepate, Mar 27 '12 at 11:27

score 3 · Accepted Answer · answered Mar 27 '12 at 14:53

I wonder if the compiler "produces" intelligent code in specific use of the new keyword. To be precise, what will it do if the new is set on a return instruction or even on operator = ?

First off you should clarify which "compiler" you mean. The C# compiler which compiles C# to IL, or the jit compiler that compiles IL to machine code?

If you want to know what the C# compiler does try it and see. Use ILDASM to view the output of the C# compiler. Remember that the /optimize switch can in some cases massively change what IL is generated.

To see what code the jitter produces, first decide which jitter is relevant to you; the compact framework, the 32 bit desktop, the 64 bit desktop, Silverlight, and so on, all have different jitters.

Next, decide whether you are interested in the debug output of the jitter or the fully optimized output.

If you want to see the fully optimized output then you have some work to do. Write a program that calls the method you want to see the code for once, and then attach the debugger to it before the second call. The jitter knows when a debugger is attached and generates different code to make it easier to debug, so if you want to know what is happening when you are not debugging, you have to trigger the jitter before it knows there is a debugger attached.

Is it okay to use "a = new type(...);" where type is a small struct in routines

1 Answers1