Read-only and write-only properties in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Read-only and write-only properties

Define Property

↓

Is it Read-only?

Yes→Only get accessor

↓

Can read value

↓

Is it Write-only?

Yes→Only set accessor

↓

Can set value

↓

Has both get and set

↓

Can read and write value

This flow shows how a property can be defined as read-only (only get), write-only (only set), or both (get and set).

Execution Sample

C Sharp (C#)

class Person {
  private string name;
  public string Name { get => name; } // Read-only
  private string secret;
  public string Secret { set => secret = value; } // Write-only
}

Defines a class with a read-only property 'Name' and a write-only property 'Secret'.

Execution Table

Step	Action	Property Accessed	Operation	Result/Effect
1	Create Person instance	-	-	Person object created with default fields
2	Set Name property	Name	set	Error: No set accessor, cannot assign
3	Get Name property	Name	get	Returns current 'name' value (default null)
4	Set Secret property	Secret	set	Sets 'secret' field to assigned value
5	Get Secret property	Secret	get	Error: No get accessor, cannot read
6	Add set accessor to Name	Name	set	Now can assign value to 'name'
7	Set Name property	Name	set	'name' field updated
8	Get Name property	Name	get	Returns updated 'name' value

💡 Execution stops after demonstrating read-only and write-only property access and errors.

Variable Tracker

Variable	Start	After Step 4	After Step 7	Final
name	null	null	"Alice"	"Alice"
secret	null	"mySecret"	"mySecret"	"mySecret"

Key Moments - 3 Insights

Why does setting the read-only property 'Name' cause an error?

Because 'Name' only has a get accessor (see step 2 in execution_table), so it cannot be assigned a value.

Why can't we read the write-only property 'Secret'?

Because 'Secret' only has a set accessor (see step 5), so reading it is not allowed and causes an error.

What changes when we add a set accessor to 'Name'?

Now 'Name' can be assigned a value (step 6 and 7), allowing both reading and writing.

Visual Quiz - 3 Questions

Look at the execution_table, what happens when we try to set the 'Name' property at step 2?

A The 'name' field is updated

B An error occurs because there is no set accessor

C The 'secret' field is updated

D The property returns null

💡 Hint

Check step 2 in the execution_table where setting 'Name' causes an error.

According to variable_tracker, what is the value of 'secret' after step 4?

A null

B "Alice"

C "mySecret"

D Error

💡 Hint

Look at the 'secret' row after step 4 in variable_tracker.

If we remove the get accessor from 'Name', what would happen when trying to read it at step 8?

A It causes an error because get accessor is missing

B It returns the current value

C It sets the value instead

D It returns null always

💡 Hint

Refer to step 5 in execution_table where missing accessor causes error.

Concept Snapshot

Read-only property: has only get accessor, can only read value.
Write-only property: has only set accessor, can only assign value.
Both get and set: property can be read and written.
Trying to access missing accessor causes compile-time error.
Use private fields to store property data.

Full Transcript

This example shows how properties in C# can be read-only or write-only. A read-only property has only a get accessor, so you can read its value but cannot assign to it. A write-only property has only a set accessor, so you can assign a value but cannot read it. Trying to use a missing accessor causes an error. Adding both get and set allows reading and writing. The variable tracker shows how the underlying fields change as properties are accessed or assigned.

Practice

1.

Which statement correctly describes a read-only property in C#?

easy

A. It has only a set accessor and no get accessor.

B. It has only a get accessor and no set accessor.

C. It has both get and set accessors.

D. It has no accessors at all.

Solution

1. Step 1: Understand property accessors

   A property with only a get accessor allows reading but not writing.

2. Step 2: Identify read-only property

   Read-only properties have no set accessor, so they cannot be assigned a value.

3. Final Answer:

   It has only a get accessor and no set accessor. -> Option B

4. Quick Check:

   Read-only = get only [OK]

Hint: Read-only means only get accessor present [OK]

Common Mistakes:

• Confusing read-only with write-only properties
• Thinking both get and set are needed for read-only
• Assuming no accessors means read-only

2.

Which of the following is the correct syntax for a write-only property named Password in C#?

public string Password { ? }

easy

A. set { _password = value; }

B. get { return _password; }

C. get; set;

D. private get; public set;

Solution

1. Step 1: Identify write-only property syntax

   A write-only property has only a set accessor to allow writing but no reading.

2. Step 2: Match syntax to write-only

   set { _password = value; } shows only a set accessor with assignment, which is correct for write-only.

3. Final Answer:

   set { _password = value; } -> Option A

4. Quick Check:

   Write-only = set only [OK]

Hint: Write-only means only set accessor present [OK]

Common Mistakes:

• Using get accessor in write-only property
• Using both get and set for write-only
• Incorrect accessor visibility modifiers

3.

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

class User {
    private string _name = "Alice";
    public string Name { get { return _name; } }
}

var user = new User();
Console.WriteLine(user.Name);

medium

A. Compilation error

B. null

C. Runtime error

D. Alice

Solution

1. Step 1: Analyze the property

   The Name property is read-only with a get accessor returning "Alice".

2. Step 2: Check output of Console.WriteLine

   Calling user.Name returns "Alice", so it prints "Alice".

3. Final Answer:

   Alice -> Option D

4. Quick Check:

   Read-only property returns stored value [OK]

Hint: Read-only property returns stored value when accessed [OK]

Common Mistakes:

• Expecting a compilation error due to missing set
• Thinking write-only properties can be read
• Confusing private field with property access

4.

Identify the error in this C# code snippet:

class Account {
    private string _pin;
    public string Pin {
        get { return _pin; }
        set { _pin = value; }
    }
}

var acc = new Account();
acc.Pin = "1234";
Console.WriteLine(acc.Pin);

The goal is to make Pin write-only.

medium

A. The private field _pin should be public.

B. The set accessor should return a value.

C. The property has both get and set accessors, so it is not write-only.

D. The property should be static.

Solution

1. Step 1: Check property accessors

   The property has both get and set accessors, allowing reading and writing.

2. Step 2: Understand write-only requirement

   Write-only properties must have only a set accessor and no get accessor.

3. Final Answer:

   The property has both get and set accessors, so it is not write-only. -> Option C

4. Quick Check:

   Write-only = set only, no get [OK]

Hint: Write-only means no get accessor allowed [OK]

Common Mistakes:

• Leaving both get and set for write-only
• Changing field visibility instead of property
• Expecting set to return a value

5.

You want to create a class Secret that stores a string value. The value should be settable but never readable from outside the class. Inside the class, you want to log the value whenever it is set. Which property implementation achieves this?

hard

A. public string Data { set { Console.WriteLine(value); _data = value; } }

B. public string Data { get { return _data; } private set { _data = value; } }

C. public string Data { get; set; }

D. public string Data { private get; set { Console.WriteLine(value); _data = value; } }

Solution

1. Step 1: Identify write-only property with logging

   The property must have only a set accessor to be write-only and log the value when set.

2. Step 2: Check each option

   public string Data { set { Console.WriteLine(value); _data = value; } } has only a set accessor that logs and assigns the value, matching requirements.

3. Final Answer:

   public string Data { set { Console.WriteLine(value); _data = value; } } -> Option A

4. Quick Check:

   Write-only with logging in set accessor [OK]

Hint: Write-only property has only set accessor with logging code [OK]

Common Mistakes:

• Adding get accessor making property readable
• Using private get instead of no get
• Not logging inside set accessor