Multiple generic parameters in C Sharp (C#)

Introduction

Using multiple generic parameters lets you create flexible code that works with different types at the same time.

When you want a class or method to handle two or more different types safely.

When you need to pair two types together, like a key and a value.

When writing reusable code that can work with many type combinations.

When you want to avoid writing the same code for different type pairs.

When creating data structures like dictionaries or tuples.

Syntax

C Sharp (C#)

class ClassName<T1, T2> {
    // Use T1 and T2 inside
}

void MethodName<T1, T2>(T1 param1, T2 param2) {
    // Use param1 and param2
}

Each generic parameter is separated by a comma inside angle brackets <>.

You can use as many generic parameters as you need.

Examples

This class stores two values of different types together.

C Sharp (C#)

class Pair<T1, T2> {
    public T1 First;
    public T2 Second;

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

This method prints two values of any types.

C Sharp (C#)

void PrintPair<T1, T2>(T1 a, T2 b) {
    Console.WriteLine($"First: {a}, Second: {b}");
}

Creating a Pair with an int and a string, then printing them.

C Sharp (C#)

var pair = new Pair<int, string>(10, "apples");
Console.WriteLine($"{pair.First} {pair.Second}");

Sample Program

This program shows a class with two generic types and a method with two generic types. It creates a pair and prints it, then calls the method with different types.

C Sharp (C#)

using System;

class Pair<T1, T2> {
    public T1 First;
    public T2 Second;

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

class Program {
    static void PrintPair<T1, T2>(T1 a, T2 b) {
        Console.WriteLine($"First: {a}, Second: {b}");
    }

    static void Main() {
        var pair = new Pair<int, string>(5, "oranges");
        Console.WriteLine($"Pair contains: {pair.First} and {pair.Second}");

        PrintPair<double, bool>(3.14, true);
    }
}

Important Notes

Generic parameters can have constraints to limit what types are allowed.

Using multiple generics helps keep code safe and reusable.

Summary

Multiple generic parameters let you work with many types at once.

They make your code flexible and reusable.

You separate generic types with commas inside <>.

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