modifiy dictionary value作为out参数和引用

Question

I want to create an Entity-Component-System example. I have components like

internal struct Position : IComponent
{
    public int X { get; set; }
    public int Y { get; set; }
}

and

internal struct Movementspeed : IComponent
{
    public float Value { get; set; }
}

which implement

internal interface IComponent
{
}

When looping through the components I want to find them as fast as possible. I thought about creating a Dictionary that takes in the components type as key and the component as value.

internal class ComponentCollection
{
    public ComponentCollection()
    {
        components = new Dictionary<Type, object>();
    }

    private Dictionary<Type, object> components;

    public void AddComponent<T>(T component) // add a new component
    {
        Type componentType = typeof(T);
        components.Add(componentType, component as IComponent);
    }

    public void RemoveComponent(Type componentType) // remove the component by type
    {
        components.Remove(componentType);
    }

    public bool TryGetComponent<T>(out T component) // get the specified component
    {
        try
        {
            Type componentType = typeof(T);
            component = (T)components[componentType];
            return true;
        }
        catch (Exception)
        {
            component = default(T);
            return false;
        }
    }
}

There are two problems that come up.

1. What if someone creates a new MovementspeedComponent using float movementspeed and tries to add it? Having two floats would throw an duplicate key exception. I could only add custom struct components which implement the IComponent interface to prevent duplicates.

2. When I try to modify the components they are not modified by reference

    private static void Main(string[] args) { ComponentCollection components = new ComponentCollection(); components.AddComponent(new Position()); components.AddComponent(new Movementspeed()); if (components.TryGetComponent(out Position fooPosition)) { fooPosition.X++; Console.WriteLine(fooPosition.X); // prints 1 } if (components.TryGetComponent(out Position barPosition)) { Console.WriteLine(barPosition.X); // prints 0 } Console.ReadLine(); } 

Any suggestions?

Answer 1

What if someone creates a new MovementspeedComponent using float movementspeed

Types are good for keys when we have one object/collection per each type otherwise a Dictionary<Type, object> isn't a good fit, key should be unique.

When I try to modify the components they are not modified by reference

Since all of components are struct s this line of code:

components.TryGetComponent(out Position fooPosition)

Gets a copy of struct that we have in the dictionary. A quote from C# guide :

Structs are copied on assignment. When a struct is assigned to a new variable, all the data is copied, and any modification to the new copy does not change the data for the original copy. This is important to remember when working with collections of value types such as Dictionary.

What if someone creates a new MovementspeedComponent using float movementspeed and tries to add it?

Answer 2

I see 2 solutions. Either use classes instead of structs or add some Update method to update struct in dictionary

public void UpdateComponent<T>(T component)
{
    Type componentType = typeof(T);
    components[componentType] = component;
}

Then call this method after you'r done with updating your struct:

if (components.TryGetComponent(out Position fooPosition))
{
    fooPosition.X++;
    components.UpdateComponent(fooPosition);
    Console.WriteLine(fooPosition.X); // prints 1
}

If you'll use classes instead of structs your old solution should work.