How to deal with the immutability of returned structs?

Question

I\'m writing a game that has a huge 2D array of \"cells\". A cell takes only 3 bytes. I also have a class called CellMap, which contains the 2D array as a private field, and pro

Answer 1

If you want to make Cell immutable - as you should if it is a struct - then a good technique is to make a factory that is an instance method on the Cell:

struct C
{
    public int Foo { get; private set; }
    public int Bar { get; private set; }
    private C (int foo, int bar) : this()
    {
        this.Foo = foo;
        this.Bar = bar;
    }
    public static C Empty = default(C);
    public C WithFoo(int foo)
    {
        return new C(foo, this.Bar);
    }
    public C WithBar(int bar)
    {
        return new C(this.Foo, bar);
    }
    public C IncrementFoo()
    {
        return new C(this.Foo + 1, bar);
    }
    // etc
}
...
C c = C.Empty;
c = c.WithFoo(10);
c = c.WithBar(20);
c = c.IncrementFoo();
// c is now 11, 20

So your code would be something like

map[x,y] = map[x,y].IncrementPopulation();

However, I think this is possibly a blind alley; it might be better to simply not have so many Cells around in the first place, rather than trying to optimize a world where there are thousands of them. I'll write up another answer on that.