How to not specify the data type of arguments?

Question

I want an Adapter like function. The parent class want DataTable, while its derived class may pass in anything. I'm now setting the data type to object and then cast it. But I do not think this is pretty.

class Parent
{
    protected void Add(DataTable dt) { ... }        // the real business logics
    public virtual void AddRaw(object anything) {}
}

class Child1 : Parent
{
    public override void AddRaw(object anything)
    {
        MyTable1 t = (MyTable1) anything;

        // pseudo code
        DataTable dt = new DataTable();
        foreach(row r in t)
        {
            dt.AddRow(r);
        }

        this.Add(dt);
    }
}

class Child2 : Parent
{
    public override void AddRaw(object anything)
    {
        MyTable2 t = (MyTable2) anything;
        ...
    }
}

I've background from javascript and python. It's so common to do such things in a "weak type" languages, and within which you can pass anything anywhere.

I've used <T> and delegate in C# before. But I cannot think of a way using them here.

What's the C# way of doing this?

void AddRaw(MyTable anything), what's wrong with this? Also, I suppose that Child derives from Parent? — BlackBear, Mar 06 '14 at 09:37
I don't really understand the problem. Why not change `public virtual void AddRaw(MyTable anything) {}` in the base class? This probably should be an abstract method anyway, or not be there at all. — Grzenio, Mar 06 '14 at 09:39
MyTable should have a common base though? BaseTable perhaps? — James, Mar 06 '14 at 09:40
@JamesBarrass. No. That's the problem. MyTable can be ANYTHING. — hbrls, Mar 06 '14 at 09:41
@hbrlovehaku _why_ can it be anything? you are explicitly casting it to a `MyTable1` so you must be pretty sure it's going to be a valid cast right? — Saeb Amini, Mar 06 '14 at 09:43
Then MyTable cannot be enumerated or adapted, it must be something your adapter class can interpret, at the very least IEnumerable — James, Mar 06 '14 at 09:43
Unfortunately, it's not restricted to `IEnumerable`. e.g. `int number; for i in range(0, number): dt.AddRow(i)` — hbrls, Mar 06 '14 at 09:49
Please, do not include information about a language used in a question title unless it wouldn't make sense without it. Tags serve this purpose. — Ondrej Janacek, Mar 06 '14 at 10:03

Patrick Hofman · Accepted Answer · 2014-03-06T09:46:36.477

3

You can use the dynamic keyword, an interface implementation or abstract base class, but I would personally prefer using as much typed members as possible.

Use of dynamic:

public override void AddRaw(dynamic anything)
{
    // pseudo code
    DataTable dt = new DataTable();
    foreach(row r in anything)
    {
        dt.AddRow(r);
    }

    this.Add(dt);
}

You can also do something like this, if you want to match anything and act based on the type:

public override void AddRaw(object anything)
{
    if (o is MyTable)
    { ... }
    else if (o is string)
    { ... }
}

edited Mar 06 '14 at 09:46

answered Mar 06 '14 at 09:40

Patrick Hofman

153,850
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Thanks! `dynamic` was exactly what I was hoping to have. But the other answers provided alternatives. I have to think about which is the best answer. – hbrls Mar 06 '14 at 10:00
@hbrlovehaku: If inheritance is an option, use that. (please... your life will not get better using `dynamic`) – Patrick Hofman Mar 06 '14 at 10:02
No, we're still discussing the requirements. – hbrls Mar 07 '14 at 03:57
This answered the original question best. However, I've not made up my mind to use this `dynamic`. – hbrls Mar 12 '14 at 07:16

score 0 · Answer 2 · answered Mar 06 '14 at 09:49

0

How about overloading your method?

class Parent
{
    protected void Add(DataTable dt) { ... }
}

class Child1:Parent
{
    public void Add(MyTable1 anything)
    {
        // pseudo code
        DataTable dt = new DataTable();
        foreach(row r in anything)
        {
            dt.AddRow(r);
        }

        this.Add(dt);
    }
}

class Child2:Parent
{
    public void Add(MyTable2 anything)
    {
        ...
    }
}

answered Mar 06 '14 at 09:49

WiiMaxx

5,322
8
51
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I may want to use delegate in the future. I'm not sure if `overloading` is OK with that. – hbrls Mar 06 '14 at 09:57
@hbrlovehaku based on [this link](http://bytes.com/topic/c-sharp/answers/533114-delegates-overloaded-methods) it should be OK – WiiMaxx Mar 06 '14 at 10:28
@hbrlovehaku [here](http://stackoverflow.com/a/3747953/1993545) is also an example how you could use a delegate – WiiMaxx Mar 06 '14 at 10:31

score 0 · Answer 3 · answered Mar 06 '14 at 09:49

You can make the parent class generic:

class Parent<T>
{
    protected void Add(DataTable dt) { ... }        // the real business logics
    public virtual void AddRaw(T anything) {}
}

class Child1 : Parent<MyTable1>
{
    public override void AddRaw(MyTable1 anything) { ... }
}

class Child2 : Parent<MyTable2>
{
    public override void AddRaw(MyTable2 anything) { ... }
}

In addition, I'd suggest to make Parent abstract, unless you really need to create Parent instances:

abstract class Parent<T>
{
    protected void Add(DataTable dt) { ... }        // the real business logics
    public abstract void AddRaw(T anything);
}

That way, the compiler ensures that every client must implement AddRaw.

You suggestion seems the most elegant. But I still have a question. What if I want to `Child : Parent`, `GrandChild : Child `? — hbrls, Mar 06 '14 at 10:26
@hbrlovehaku: You can't. And you don't want to. Please explain in plain English what this would mean. You can't... — Patrick Hofman, Mar 06 '14 at 10:30

score 0 · Answer 4 · answered Mar 06 '14 at 10:02

I think I'd use an adapter resolver class. Create each adapter in their own class and register them with a static class along with the type they adapter

Adapters.Register(typeof(MyTable), MyTableAdapter)

or // void Register(Adapter) and MyTableAdapter: Adapter Adapters.Register(MyTableAdapter)

then you'd request an adapter from the the Adapters list

Adapters.GetAdapter<MyTable>();

where you could return a sensible error if no adapters for that type had been registered

How to not specify the data type of arguments?

4 Answers4