C# Generic - Convert this function?

Question

3.20/5 (2 votes)

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I am very green when it comes to generics.

Can I convert a function like this to a generic one, and if so can someone give me an example implementation of it?

C#

public Dictionary<Sheet, bool> DeleteSheets(List<Sheet> sheets)
        {
            Dictionary<Sheet, bool> results = new Dictionary<Sheet, bool>();
            foreach (Sheet s in sheets)
                results.Add(s, DeleteSheet(s));

            return results;
        }

I have several functions just like this, except the return value, method parameter, and the method called in the .Add function are different types.

Like I said, I am green when it comes to this....

Thanks!

Posted 20-Dec-13 5:12am

David Knechtges

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BillWoodruff 20-Dec-13 11:37am

This is a recursive function: a new Dictionary<Sheet, bool> is declared every time it is evaluated.

Is a 'Sheet a List<Sheet> ? I think to respond helpfully we really need to know the structure of 'Sheet.

3 solutions

Solution 1

Just replace the type you want to be generic with a letter (the convention is T):

C#

public Dictionary<T, bool> DeleteSheets(List<T> sheets)
        {
            Dictionary<T, bool> results = new Dictionary<T, bool>();
            foreach (T s in sheets)
                results.Add(s, DeleteSheet(s));

            return results;
        }

Posted 20-Dec-13 5:20am

Mehdi Gholam

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OriginalGriff · Accepted Answer · 2013-12-20T05:21:00

Try:

C#

public Dictionary<T, bool> DeleteSheets<T>(List<T> data)
    {
    Dictionary<T, bool> results = new Dictionary<T, bool>();
    foreach (T s in data)
        results.Add(s, Delete<T>(s));

    return results;
    }
public bool Delete<T>(T s) { return true; }

Griff,

The Delete method executes different code, based on what function it is, but they all return bools. How can I handle that? Use a delegate for this?

That's not as simple as it sounds: you can use a Delegate:

C#

Dictionary<string, bool> data = DeleteSheets(new List<string>() { "hello", "goodbye" }, DeleteString);
    Dictionary<int, bool> data2 = DeleteSheets(new List<int>() { 1, 2, 3 }, DeleteString);
    }

bool DeleteString(string s) { Console.WriteLine(s); return true; }
bool DeleteString(int s) { Console.WriteLine("Del" + s ); return true; }
public delegate bool DeleteMethod<T>(T t);
public Dictionary<T, bool> DeleteSheets<T>(List<T> data, DeleteMethod<T> delete ) //where T: Base
    {
    Dictionary<T, bool> results = new Dictionary<T, bool>();
    foreach (T s in data)
        results.Add(s, delete(s));

    return results;
    }

And it will call the appropriate method.

But I'd rather restrict the generic to a base class and do it via overloading instead:

C#

Dictionary<Base, bool> data2 = DeleteSheets(new List<Base>() { new A(), new A(), new B() });
    }

public Dictionary<T, bool> DeleteSheets<T>(List<T> data ) where T: Base
    {
    Dictionary<T, bool> results = new Dictionary<T, bool>();
    foreach (T s in data)
        results.Add(s, s.Delete());

    return results;
    }
public abstract class Base
    {
    public abstract bool Delete();
    }
public class A : Base
    {
    public override bool Delete()
        {
        Console.WriteLine("A Delete");
        return true;
        }
    }
public class B : Base
    {
    public override bool Delete()
        {
        Console.WriteLine("B Delete");
        return true;
        }
    }

It just seems like a "cleaner" solution.

bowlturner · Accepted Answer · 2013-12-20T05:26:00

Solution 3

This should be close to what you are looking for. Not sure what the DeleteSheets() in the foreach is supposed to do. If I did I might be able to help there too.

Made changes to take the DeleteSheet func as a parameter.

C#

public Dictionary<T, bool> DeleteSheets<T>(List<T> sheets, Func<T, bool> delT)
       {
           Dictionary<T, bool> results = new Dictionary<T, bool>();
           foreach (T s in sheets)
               results.Add(s, delT(s));

           return results;
       }

Posted 20-Dec-13 5:26am

bowlturner

Updated 20-Dec-13 5:36am

v2

Comments

David Knechtges 20-Dec-13 11:37am

DeleteSheet represents a method that is called. They all have different functionality, but all return a bool. Should I use a delegate for this and pass the delegate to the generic method?

bowlturner 20-Dec-13 11:43am

I changed it to take a delegate, it takes a <t> and returns a bool

David Knechtges 20-Dec-13 11:41am

That worked perfectly for me.... Thank you very much!

bowlturner 20-Dec-13 11:44am

your welcome.