Generic method declaration in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a generic method named 'PrintItem' that takes one parameter of type T.

C Sharp (C#)

public void [1]<T>(T item) {
    Console.WriteLine(item);
}

Drag options to blanks, or click blank then click option'

APrintItem

BDisplay

CShowItem

DPrint

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add after the method name.

Using a different method name than 'PrintItem'.

The method name must be 'PrintItem' as specified. The generic type parameter follows the method name.

2fill in blank

medium

Complete the code to declare a generic method 'GetDefault' that returns the default value of type T.

C Sharp (C#)

public T [1]<T>() {
    return default(T);
}

Drag options to blanks, or click blank then click option'

AGetDefault

BDefaultValue

CGetValue

DFetchDefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not match the requirement.

Forgetting to specify the generic type parameter .

The method name must be 'GetDefault' to match the requirement and return the default value of type T.

3fill in blank

hard

Fix the error in the generic method declaration by completing the method name correctly.

C Sharp (C#)

public void [1]<T>(T value) {
    Console.WriteLine(value);
}

Drag options to blanks, or click blank then click option'

APrintVal

BPrintValue

CPrint

DDisplayValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that is incomplete or misspelled.

Omitting the generic type parameter .

The correct method name is 'PrintValue' to match the intended usage and avoid errors.

4fill in blank

hard

Fill both blanks to declare a generic method 'Swap' that swaps two variables of type T using ref parameters.

C Sharp (C#)

public void [1]<T>(ref T a, ref T [2]) {
    T temp = a;
    a = [2];
    [2] = temp;
}

Drag options to blanks, or click blank then click option'

ASwap

BSwapValues

Cb

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names.

Using a method name that does not describe swapping.

The method name is 'Swap' and the second parameter name is 'b' to correctly swap two variables.

5fill in blank

hard

Fill all three blanks to declare a generic method 'CreatePair' that returns a Tuple of two generic types T1 and T2.

C Sharp (C#)

public Tuple<[1], [2]> [3]<T1, T2>(T1 first, T2 second) {
    return Tuple.Create(first, second);
}

Drag options to blanks, or click blank then click option'

AT1

BT2

CCreatePair

DMakePair

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up generic type parameters.

Using a method name that does not match the tuple creation.

The generic types are T1 and T2, and the method name is 'CreatePair' to return a tuple of two values.

Practice

1. What is the purpose of declaring a generic method in C# using <T>?

easy

A. To allow the method to work with any data type specified when called

B. To restrict the method to only work with integers

C. To make the method private

D. To declare a method that returns void only

Solution

1. Step 1: Understand generic method declaration

   Generic methods use <T> to represent a placeholder for any type, making the method flexible.

2. Step 2: Identify the purpose of <T>

   The <T> allows the method to accept or return any type specified at call time, improving reuse.

3. Final Answer:

   To allow the method to work with any data type specified when called -> Option A

4. Quick Check:

   Generic <T> means flexible type [OK]

Hint: Generic <T> means method works with any type [OK]

Common Mistakes:

• Thinking <T> restricts to one type like int
• Confusing generic methods with access modifiers
• Assuming generic methods always return void

2. Which of the following is the correct syntax to declare a generic method named PrintItem that takes one parameter of type T?

easy

A. public void PrintItem<T>(item T) { Console.WriteLine(item); }

B. public <T> void PrintItem(T item) { Console.WriteLine(item); }

C. public void PrintItem<T>(T item) { Console.WriteLine(item); }

D. public void PrintItem(T item) { Console.WriteLine(item); }

Solution

1. Step 1: Review generic method syntax

   The generic type parameter <T> must come immediately after the method name.

2. Step 2: Check parameter declaration

   The parameter should be declared as type T, followed by the parameter name.

3. Final Answer:

   public void PrintItem<T>(T item) { Console.WriteLine(item); } -> Option C

4. Quick Check:

   Generic <T> after method name, parameter type T [OK]

Hint: Put <T> right after method name for generics [OK]

Common Mistakes:

• Placing <T> before return type
• Omitting <T> after method name
• Swapping parameter type and name

3. What will be the output of the following code?

public class Program {
    public static void ShowType<T>(T value) {
        Console.WriteLine(typeof(T));
    }
    public static void Main() {
        ShowType(123);
        ShowType("hello");
    }
}

medium

A. 123
hello

B. System.Int32
System.String

C. T
T

D. System.Object
System.Object

Solution

1. Step 1: Understand typeof(T) in generic method

   typeof(T) returns the actual type used when the method is called.

2. Step 2: Analyze calls ShowType(123) and ShowType("hello")

   First call uses int (System.Int32), second uses string (System.String).

3. Final Answer:

   System.Int32 System.String -> Option B

4. Quick Check:

   typeof(T) shows actual type [OK]

Hint: typeof(T) prints actual type used at call [OK]

Common Mistakes:

• Expecting value output instead of type
• Thinking T is printed literally
• Assuming typeof(T) always returns System.Object

4. Identify the error in this generic method declaration:

public void Swap<T>(T a, T b) {
    T temp = a;
    a = b;
    b = temp;
}

medium

A. Cannot declare variable temp of type T

B. Missing generic type declaration <T> after method name

C. Method must return a value to swap

D. Cannot swap values because parameters are passed by value

Solution

1. Step 1: Check parameter passing

   Parameters a and b are passed by value, so swapping inside method won't affect caller.

2. Step 2: Confirm generic syntax correctness

   The method correctly declares <T> after method name and uses T type variables.

3. Final Answer:

   Cannot swap values because parameters are passed by value -> Option D

4. Quick Check:

   Value parameters can't swap caller variables [OK]

Hint: Swap needs ref/out to affect caller variables [OK]

Common Mistakes:

• Thinking generic syntax is wrong
• Assuming temp can't be type T
• Expecting method must return swapped values

5. You want to write a generic method FindMax that returns the maximum of two values of any type T. Which constraint should you add to T to make comparison possible?

hard

A. where T : IComparable<T>

B. where T : class

C. where T : new()

D. where T : struct

Solution

1. Step 1: Understand comparison requirement

   To compare two values of type T, T must support comparison operations.

2. Step 2: Identify suitable generic constraint

   IComparable<T> interface defines CompareTo method for comparing instances.

3. Step 3: Review other constraints

   class restricts to reference types, new() requires parameterless constructor, struct restricts to value types but no comparison guarantee.

4. Final Answer:

   where T : IComparable<T> -> Option A

5. Quick Check:

   Use IComparable<T> to enable comparisons [OK]

Hint: Use IComparable<T> constraint for comparing generics [OK]

Common Mistakes:

• Using class or struct constraints instead of IComparable
• Forgetting to add any constraint
• Assuming new() enables comparison