Value equality in records in C Sharp (C#) - Mini Project: Build & Apply

Value equality in records

📖 Scenario: Imagine you are creating a simple contact list app. You want to store contacts as records and check if two contacts are the same based on their values.

🎯 Goal: Build a C# program that creates two contact records with the same data and checks if they are equal using value equality.

📋 What You'll Learn

Create a record named Contact with two properties: string Name and string Phone.

Create two Contact objects with the same Name and Phone values.

Compare the two Contact objects using the == operator.

Print "Equal" if they are equal, otherwise print "Not Equal".

💡 Why This Matters

🌍 Real World

Records are useful for storing data where you want to compare objects by their content, like contacts, products, or settings.

💼 Career

Understanding value equality in records helps in writing clean, bug-free code for data models in business applications.

1

Create the Contact record

Create a record called Contact with two properties: string Name and string Phone.

C Sharp (C#)

// Your code here

Hint

Use the record keyword to define a record with positional parameters.

2

Create two Contact objects with the same values

Create two Contact objects named contact1 and contact2 with Name set to "Alice" and Phone set to "12345".

C Sharp (C#)

public record Contact(string Name, string Phone);

// Your code here

Hint

Use the new keyword to create objects from the Contact record.

3

Compare the two Contact objects using value equality

Use an if statement to compare contact1 and contact2 using the == operator.

C Sharp (C#)

public record Contact(string Name, string Phone);

Contact contact1 = new Contact("Alice", "12345");
Contact contact2 = new Contact("Alice", "12345");

// Your code here

Hint

Records in C# support value equality with the == operator by default.

4

Print the comparison result

Inside the if statement, print "Equal". Inside the else, print "Not Equal".

C Sharp (C#)

public record Contact(string Name, string Phone);

Contact contact1 = new Contact("Alice", "12345");
Contact contact2 = new Contact("Alice", "12345");

if (contact1 == contact2)
{
    // Your code here
}
else
{
    // Your code here
}

Hint

Use Console.WriteLine to print the result.

Practice

1. What is the main feature of record types in C# regarding equality?

easy

A. They require manual implementation of equality methods.

B. They compare objects by their memory address only.

C. They cannot be compared for equality.

D. They compare objects by their data automatically.

Solution

1. Step 1: Understand record equality behavior

   Records in C# automatically implement value equality, meaning two records with the same data are considered equal.

2. Step 2: Contrast with normal classes

   Normal classes compare by reference (memory address) unless equality is overridden manually.

3. Final Answer:

   They compare objects by their data automatically. -> Option D

4. Quick Check:

   Record equality = value-based [OK]

Hint: Records compare data, not references, by default [OK]

Common Mistakes:

• Thinking records compare by reference like classes
• Assuming manual equality override is needed
• Believing records cannot be compared

2. Which of the following is the correct syntax to declare a positional record in C#?

easy

A. class Person { public string Name; }

B. record Person { string Name; }

C. record Person(string Name);

D. struct Person(string Name);

Solution

1. Step 1: Identify record declaration syntax

   The concise syntax for a record with a positional parameter is record Person(string Name);.

2. Step 2: Check other options

   class Person { public string Name; } is a class, not a record. struct Person(string Name); is a struct, not a record. record Person { string Name; } is invalid because positional parameters require parentheses.

3. Final Answer:

   record Person(string Name); -> Option C

4. Quick Check:

   Record syntax = record Name(params) [OK]

Hint: Use 'record Name(params);' for simple record declaration [OK]

Common Mistakes:

• Using class instead of record
• Missing parentheses for positional parameters
• Confusing struct with record

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

record Point(int X, int Y);

var p1 = new Point(3, 4);
var p2 = new Point(3, 4);
Console.WriteLine(p1 == p2);

medium

A. True

B. Compilation error

C. False

D. Runtime exception

Solution

1. Step 1: Understand record equality operator

   Records override the equality operator to compare values, so p1 == p2 compares the data inside the records.

2. Step 2: Compare values of p1 and p2

   Both have X=3 and Y=4, so they are equal and the output is True.

3. Final Answer:

   True -> Option A

4. Quick Check:

   Records with same data == True [OK]

Hint: Records compare data with == operator automatically [OK]

Common Mistakes:

• Assuming == compares references for records
• Expecting compilation error due to operator
• Thinking output is False because objects differ

4. Identify the error in this code snippet:

record Person(string Name);

var p1 = new Person("Alice");
var p2 = new Person("Alice");

if (p1.Equals(p2))
    Console.WriteLine("Equal");
else
    Console.WriteLine("Not Equal");

p1.Name = "Bob";

medium

A. Records cannot use Equals method.

B. Cannot assign to 'Name' because it is init-only.

C. Missing semicolon after record declaration.

D. p1 and p2 are different objects, so Equals returns false.

Solution

1. Step 1: Check mutability of record properties

   By default, positional record properties are immutable (init-only), so p1.Name = "Bob"; causes a compile error.

2. Step 2: Verify other statements

   Using Equals is valid and compares values correctly. The semicolon after record declaration is present. Equals returns true because data matches.

3. Final Answer:

   Cannot assign to 'Name' because it is init-only. -> Option B

4. Quick Check:

   Record properties are immutable by default [OK]

Hint: Record properties are init-only; cannot assign after creation [OK]

Common Mistakes:

• Trying to modify record properties after creation
• Thinking Equals compares references
• Ignoring immutability of positional properties

5. Given two records record Product(int Id, string Name);, how can you create a new record from an existing one but with a different Name while keeping Id the same?

hard

A. Use the 'with' expression: var p2 = p1 with { Name = "NewName" };

B. Create a new record manually: var p2 = new Product(p1.Name, "NewName");

C. Assign directly: p1.Name = "NewName";

D. Use a method to clone and change: var p2 = p1.Clone("NewName");

Solution

1. Step 1: Understand the 'with' expression for records

   The 'with' expression creates a copy of a record with specified properties changed.

2. Step 2: Compare options

   Use the 'with' expression: var p2 = p1 with { Name = "NewName" }; uses 'with' correctly. Create a new record manually: var p2 = new Product(p1.Name, "NewName"); fails to compile because Id expects int but p1.Name is string. Assign directly: p1.Name = "NewName"; is invalid because record properties are immutable. Use a method to clone and change: var p2 = p1.Clone("NewName"); is invalid as no Clone method exists by default.

3. Final Answer:

   Use the 'with' expression: var p2 = p1 with { Name = "NewName" }; -> Option A

4. Quick Check:

   'with' creates modified record copies [OK]

Hint: Use 'with' to copy and change record properties easily [OK]

Common Mistakes:

• Trying to assign directly to immutable properties
• Not using 'with' for copying records
• Assuming a Clone method exists by default