Generic class with multiple parameters in C#

Question

Ok, I know from documentation (from here and here) how to write simple generic classes with generic methods. But in my case I have something different and I'm not sure what is the right way to implement this. So this is what I have in semi pseudo-code

// This is a base class
public class Parent_Class<T>{
   T field_1;
   public void method_1<T2>(){
       T2 local_variable = new T2();
   }
}
// ^^^ Is it right?? And is it possible to inherit from this class in this way (option 1):

public Child_Class : Parent_Class <Class_1>{
    public void method_1(){
        base.method_1<Class_2>();
        // ^^^ will this work???
    }
}

And I see another alternative which may look in semi pseudo-code like this:

// This is a base class
public class Parent_Class<T, T2>{
   T field_1;
   public void method_1<T2>(){
       T2 local_variable = new T2();
   }
   // ^^^ should it be declared like public void method_1<T2>
   // or can we simply declare it with public void method_1(){
}
// ^^^ Is it right?? And is it possible to inherit from this class in this way (option 1):

public Child_Class : Parent_Class <Class_1, Class_2>{
    public void method_1(){
        base.method_1<Class_2>();
        // ^^^ should I call it like this? or can I do simply 
        //base.method_1();
    }
}

So, as you can see there is a mixture of generic types. I put my questions in the code and hope someone can point me to the right direction. Thanks!

The code look plausible (and may even compile), but you did not said what you actually want to achieve... or why you expect this code to fail/not do what you want. — Alexei Levenkov, Nov 07 '15 at 07:07
@Alexei Levenkov. Since I see two ways of creating a Parent class and inheriting from it and I see various options of how to call the Parent method from the Child class, I'm not sure what combination will work, is better and used in practice. — Jacobian, Nov 07 '15 at 07:09
Both options will work. However, a type listed as generic parameter usually appears either in the signature of the generic method or as a return type. What you are trying to do can be easily achieved without generics at all. — alexm, Nov 07 '15 at 07:14
`C` and `C` approaches are different and serve different needs - how do you expect SO to decide which one would work for *your* case? Both variants are good and used in practice. — Alexei Levenkov, Nov 07 '15 at 07:15
@Alexei. Can you please elaborate a bit on this in the format of answer - to explain why they serve different needs and why one way is preferable to another in different contexts? I will definitely accept this answer! — Jacobian, Nov 07 '15 at 07:17
You write two sets of base-derived class yourself (actual C# code, not pseudo code) in the two formats `BaseClass` & `BaseClass`, you'll understand most of the differences yourself. — Arghya C, Nov 07 '15 at 07:23
@Jacobian Though you are showing only pseudo-code but I can see some wrong code intention. For e.g: you can't new up a generic type unless you specify default constructor constraint on that type or you need to use `default(T)`. If you use Generic-Type argument across the class without new Generic-Types defined on the methods, then your contract is clear that all the methods in the class will work with declaring type only. I suggest you once again go through this [MSDN](https://msdn.microsoft.com/en-us/library/d5x73970.aspx) — Siva Gopal, Nov 07 '15 at 07:33

Acha Bill · Accepted Answer · 2015-11-07T09:17:25.383

1

Since the problem has reduced to passing args to template type constructor..

using System;

class A
{
    public A() { }
}  
class B
{
    private int data;
    public B() { }
    public B(int x) { data = x; }
    public int Data { get { return data; } }
}
class Base<T1, T2> where T2 : new()
{
    private T1 a;
    public void Method(object[] args)
    {
        //pass args to T2 constructor 
        T2 b = (T2)Activator.CreateInstance(typeof(T2), args);
    }
}
class Derived : Base<A,B>
{
    public new void Method(object[] args)
    {
        base.Method(args); 
    }
}
class Test
{
    static void Main()
    {
        Derived d = new Derived();
        d.Method(new object[]{ 1 });
    }
}

edited Nov 07 '15 at 09:17

answered Nov 07 '15 at 07:47

Acha Bill

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Thank you, sir! But can you please touch a more general case when instead of standard parameters like `char `or `int` in your example we use custom/user defined classes. I'm asking this, because I'm not sure how to transform this `T2 y = default(T2);` to something like `T2 y = new T2(param1, param2)` - I tried it hard, but was not able to implement this. – Jacobian Nov 07 '15 at 07:55
`T2 y = new T2(param 1,param 2)` will work if T2 has `new () ` constraint – Acha Bill Nov 07 '15 at 08:02
I added `new()` constraint, but get an error message, that `TestClass must have a public parameterless constructor ....`. So, I'm not able to so something like `T2 y = new T2(1)`. To add to it coustructor of `TestClass` in my case has parameters: `public TestClass(int a){...`. So, I'm not sure how to tackle this – Jacobian Nov 07 '15 at 08:06
So, when a custom/user defined class has a constructor with no parameters, then `T2 y = new T2()` works (indeed we add `new()` constraint to do that). But if the constructor has parameters, then a lot of errors pop up. – Jacobian Nov 07 '15 at 08:09
http://stackoverflow.com/questions/840261/passing-arguments-to-c-sharp-generic-new-of-templated-type will solve your problem – Acha Bill Nov 07 '15 at 09:05

Generic class with multiple parameters in C#

1 Answers1