Question

Greetings everyone!

I’ll try to make my problem simple: I have an enum to select which ObjType I should use (ObjTypeA and ObjTypeB both inherits from ObjType). So I created a method to extend the given enum, in order to return a new instance according to the selected property in the enum, like follows in the code. I think it works more or less like a factory design pattern. So far so good, but eventually, like in the class MyClass, I may attempt to create n instances of ObjTypeA or ObjTypeB, but I’ll have to face the if statement everytime I call the GetObjTypeInstance() method. So:

• Can an enum return an instance, something like: public enum EObjType { ObjTypeA = new ObjTypeA(), ObjTypeB = new ObjTypeB() }? Actually, it’d be better to append some GetInstance() method to the ObjTypeA and to the ObjTypeB options in the enum. If there’s a way to do this, how can I do it? Doing this I’d avoid those if statements every while step.
• Is there any other (and better) way to this this (if you understood my problem…)? How?

Thanks in advance!

Follow the example code:

public static class EObjTypeExt
{
    public static ObjType GetObjTypeInstance(this EObjType ot)
    {
        if (ot == EObjType.ObjTypeA)
        {
            return new ObjTypeA();
        }
        else if (ot == EObjType.ObjTypeB)
        {
            return new ObjTypeB();
        }
        throw new ArgumentOutOfRangeException("unrecognized type!");
    }
}

public enum EObjType { ObjTypeA, ObjTypeB }

public class MyClass
{
    ObjType[] obj { get; set; }

    public MyClass(EObjType otEnum, int n)
    {
        this.obj = new ObjType[n];
        int i = 0;
        while (i < n)
        {
            this.obj[i] = otEnum.GetObjTypeInstance();
            i++;
        }
    }
}

Answer 1

Instead of using an enum, I would use a class that looks like an enum:

public class EObjType {
    public static readonly EObjType ObjTypeA = new EObjType(() => (ObjType)(new ObjTypeA));
    public static readonly EObjType ObjTypeB = new EObjType(() => (ObjType)(new ObjTypeB));

    private readonly Func<ObjType> generator;
    private EObjType(Func<ObjType> generator) {
        this.generator = generator;
    }

    public ObjType GetInstanceOfObjType() {
        return generator();
    }
}

You can then use it exactly as you have been the enum.

EObjType otEnum = EObjType.ObjTypeA;
ObjType obj = otEnum.GetInstanceOfObjType();