Multiple generic parameters in C Sharp (C#) - Mini Project: Build & Apply

Using Multiple Generic Parameters in C#

📖 Scenario: You are building a simple container class that can hold two different types of items together, like a box with two compartments.

🎯 Goal: Create a generic class with two type parameters and use it to store and display two different values.

📋 What You'll Learn

Create a generic class called Pair with two generic type parameters: T1 and T2.

Add two public fields: First of type T1 and Second of type T2.

Create a constructor that takes two parameters to initialize First and Second.

Create an instance of Pair with string and int types.

Print the values of First and Second.

💡 Why This Matters

🌍 Real World

Generic classes with multiple type parameters are useful when you want to group two related but different types of data together, like a key-value pair or a coordinate point.

💼 Career

Understanding multiple generic parameters helps in writing flexible and reusable code, which is important in software development jobs that require designing libraries, APIs, or data structures.

1

Create the generic class with two type parameters

Create a generic class called Pair with two generic type parameters T1 and T2. Inside the class, declare two public fields: First of type T1 and Second of type T2.

C Sharp (C#)

public class Pair
{
    // Your code here
}

Hint

Use public class Pair<T1, T2> to declare the class with two generic parameters.

2

Add a constructor to initialize the fields

Add a constructor to the Pair class that takes two parameters: first of type T1 and second of type T2. Inside the constructor, set the fields First and Second to these parameters.

C Sharp (C#)

public class Pair
{
    public T1 First;
    public T2 Second;

    // Add constructor here
    // Your code here
}

Hint

Constructor name must match the class name Pair. Assign parameters to fields inside the constructor.

3

Create an instance of the generic class

In the Main method, create an instance of Pair with string as T1 and int as T2. Name the variable myPair and initialize it with the values "apple" and 5.

C Sharp (C#)

public class Pair
{
    public T1 First;
    public T2 Second;

    public Pair(T1 first, T2 second)
    {
        First = first;
        Second = second;
    }
}

class Program
{
    static void Main()
    {
        // Create instance of Pair called myPair
        // Your code here
    }
}

Hint

Use new Pair<string, int>("apple", 5) to create the instance.

4

Print the values of the generic fields

Add two Console.WriteLine statements in the Main method to print the values of myPair.First and myPair.Second.

C Sharp (C#)

public class Pair
{
    public T1 First;
    public T2 Second;

    public Pair(T1 first, T2 second)
    {
        First = first;
        Second = second;
    }
}

class Program
{
    static void Main()
    {
        Pair myPair = new Pair("apple", 5);
        // Print myPair.First and myPair.Second
        // Your code here
    }
}

Hint

Use Console.WriteLine(myPair.First); and Console.WriteLine(myPair.Second); to print the values.

Practice

1.

What is the correct way to declare a generic class with two type parameters in C#?

class MyClass<T1, T2> { }

easy

A. class MyClass<T1> { }

B. class MyClass<T1, T2> { }

C. class MyClass<T1; T2> { }

D. class MyClass<T1 T2> { }

Solution

1. Step 1: Understand generic class syntax

   In C#, multiple generic parameters are separated by commas inside angle brackets <>.

2. Step 2: Check each option's syntax

   class MyClass<T1, T2> { } correctly uses a comma between T1 and T2. Other options use a single parameter, semicolon, or space which are incorrect.

3. Final Answer:

   class MyClass<T1, T2> { } -> Option B

4. Quick Check:

   Multiple generic parameters use commas inside <> [OK]

Hint: Separate generic types with commas inside angle brackets [OK]

Common Mistakes:

• Using semicolons or spaces instead of commas
• Forgetting to separate multiple generic parameters
• Declaring only one generic parameter when two are needed

2.

Which of the following is the correct syntax to declare a method with two generic parameters in C#?

public void Swap<T1, T2>(T1 a, T2 b) { }

easy

A. public void Swap<T1 T2>(T1 a, T2 b) { }

B. public void Swap<T1; T2>(T1 a, T2 b) { }

C. public void Swap<T1, T2>(T1 a, T2 b) { }

D. public void Swap(T1 a, T2 b) { }

Solution

1. Step 1: Recall method generic parameter syntax

   Generic parameters for methods are declared inside angle brackets <> separated by commas.

2. Step 2: Evaluate each option

   public void Swap<T1, T2>(T1 a, T2 b) { } correctly uses commas between T1 and T2. Other options use invalid separators like space or semicolon, or miss the generic parameters entirely.

3. Final Answer:

   public void Swap<T1, T2>(T1 a, T2 b) { } -> Option C

4. Quick Check:

   Method generics need commas inside <> [OK]

Hint: Use commas to separate generic parameters in method declarations [OK]

Common Mistakes:

• Omitting generic parameters in method signature
• Using spaces or semicolons instead of commas
• Placing generic parameters outside angle brackets

3.

What will be the output of the following C# code?

class Pair<T1, T2> {
    public T1 First;
    public T2 Second;
    public Pair(T1 first, T2 second) {
        First = first;
        Second = second;
    }
    public override string ToString() {
        return $"{First} and {Second}";
    }
}

var p = new Pair<int, string>(5, "hello");
Console.WriteLine(p);

medium

A. 5, hello

B. Pair`2

C. System.Pair

D. 5 and hello

Solution

1. Step 1: Understand the Pair class and ToString override

   The Pair class stores two values and overrides ToString to return "{First} and {Second}".

2. Step 2: Analyze the instantiation and output

   We create Pair<int, string> with 5 and "hello". Console.WriteLine calls ToString, so output is "5 and hello".

3. Final Answer:

   5 and hello -> Option D

4. Quick Check:

   ToString returns "{First} and {Second}" [OK]

Hint: Check ToString override for output format [OK]

Common Mistakes:

• Assuming default ToString output for generic class
• Confusing comma with 'and' in output
• Ignoring ToString override

4.

Identify the error in the following code snippet:

class Container<T1, T2> {
    public T1 Item1;
    public T2 Item2;
    public Container(T1 item1, T2 item2) {
        Item1 = item1;
        Item2 = item2;
    }
}

var c = new Container<int>(5, 10);

medium

A. Missing second generic type argument when creating Container instance

B. Constructor parameters types do not match generic types

C. Cannot use int as generic type

D. Missing semicolon after class declaration

Solution

1. Step 1: Check generic parameters in class and instance

   The class Container requires two generic types: T1 and T2.

2. Step 2: Analyze the instance creation

   The code uses Container<int> with only one generic argument, but two are required.

3. Final Answer:

   Missing second generic type argument when creating Container instance -> Option A

4. Quick Check:

   Two generic parameters require two type arguments [OK]

Hint: Match number of generic arguments with parameters [OK]

Common Mistakes:

• Providing fewer generic arguments than declared
• Assuming default generic types
• Ignoring compiler errors about generic arguments

5.

Given the following generic method, what is the correct way to call it with two different types?

public static void PrintPair<T1, T2>(T1 first, T2 second) {
    Console.WriteLine($"First: {first}, Second: {second}");
}

Choose the correct call:

hard

A. PrintPair<int, string>(10, "test");

B. PrintPair<int>(10, "test");

C. PrintPair<T1, T2>(10, "test");

D. PrintPair<string, int>(10, "test");

Solution

1. Step 1: Understand generic method call syntax

   When calling a generic method with multiple parameters, specify all types inside <> in order.

2. Step 2: Match types with arguments

   The method expects T1 then T2. PrintPair<int, string>(10, "test"); uses <int, string> matching arguments 10 (int) and "test" (string). PrintPair<string, int>(10, "test"); reverses types incorrectly.

3. Final Answer:

   PrintPair<int, string>(10, "test"); -> Option A

4. Quick Check:

   Generic method call types match argument order [OK]

Hint: Specify all generic types in order when calling method [OK]

Common Mistakes:

• Providing fewer generic types than parameters
• Reversing generic types order
• Omitting generic types when required