Handle vs value classes in MATLAB - Visual Side-by-Side Comparison

Concept Flow - Handle vs value classes

Create object

↓

Is it handle class?

No→Value class: copy on assignment

↓

Modify copy

↓

Modify object

↓

All references see change

↓

End

This flow shows how MATLAB treats handle classes by reference and value classes by copying on assignment.

Execution Sample

MATLAB

classdef MyHandle < handle
  properties
    Data
  end
end

obj1 = MyHandle;
obj1.Data = 10;
obj2 = obj1;
obj2.Data = 20;

This code creates a handle class object, assigns it to two variables, and modifies the data through one variable.

Execution Table

Step	Action	Variable States	Explanation
1	Create obj1 of MyHandle	obj1.Data = []	obj1 is created with empty Data
2	Set obj1.Data = 10	obj1.Data = 10	Data property of obj1 set to 10
3	Assign obj2 = obj1	obj2.Data = 10	obj2 references same object as obj1 (handle)
4	Set obj2.Data = 20	obj1.Data = 20, obj2.Data = 20	Both see change because same object
5	End	obj1.Data = 20, obj2.Data = 20	Execution ends, both variables reference same updated object

💡 Execution stops after modifying obj2.Data; both obj1 and obj2 reflect the change because it's a handle class.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
obj1.Data	[]	10	10	20	20
obj2.Data	N/A	N/A	10	20	20

Key Moments - 2 Insights

Why do obj1.Data and obj2.Data both change to 20 after modifying obj2.Data?

Because obj1 and obj2 reference the same handle object, changing Data via obj2 affects obj1 too, as shown in execution_table step 4.

What would happen if MyHandle was a value class instead of a handle class?

Assigning obj2 = obj1 would create a copy, so modifying obj2.Data would not affect obj1.Data, unlike the handle class behavior in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of obj2.Data?

A []

B 20

C 10

D Undefined

💡 Hint

Check the Variable States column at step 3 in execution_table.

At which step do obj1.Data and obj2.Data first differ?

A They never differ

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the Variable States columns for obj1.Data and obj2.Data across all steps.

If MyHandle was a value class, what would obj1.Data be after step 4?

A 20

B 10

C []

D Undefined

💡 Hint

Recall that value classes copy on assignment, so modifying obj2.Data does not affect obj1.Data.

Concept Snapshot

Handle classes in MATLAB behave like references: multiple variables point to the same object, so changes affect all references.
Value classes behave like copies: assigning creates a new object, so changes to one do not affect others.
Use < handle > to define handle classes.
Assigning handle objects copies the reference, not the object.
Assigning value objects copies the object itself.

Full Transcript

This visual execution shows how MATLAB handle classes differ from value classes. When you create a handle class object and assign it to two variables, both variables point to the same object. Changing a property through one variable changes it for the other too. This is because handle classes are passed by reference. In contrast, value classes copy the object on assignment, so changes to one copy do not affect the other. The execution table traces creating a handle object, assigning it, and modifying its property, showing both variables reflect the change. The variable tracker confirms the property values step-by-step. Key moments clarify why both variables change together and what would happen with value classes. The quiz tests understanding of these behaviors by referencing the execution steps and variable states.

Practice

1. Which statement correctly describes the difference between handle and value classes in MATLAB?

easy

A. Handle classes share data between copies, while value classes keep data separate.

B. Value classes share data between copies, while handle classes keep data separate.

C. Both handle and value classes always share data between copies.

D. Both handle and value classes always keep data separate for each copy.

Solution

1. Step 1: Understand handle class behavior

   Handle classes in MATLAB share the same data when copied, meaning changes to one copy affect all copies.

2. Step 2: Understand value class behavior

   Value classes create independent copies, so changes to one copy do not affect others.

3. Final Answer:

   Handle classes share data between copies, while value classes keep data separate. -> Option A

4. Quick Check:

   Handle = shared, Value = separate [OK]

Hint: Remember: handle = shared data, value = independent copies [OK]

Common Mistakes:

• Confusing which class shares data
• Thinking both classes behave the same
• Assuming handle classes create independent copies

2. Which of the following is the correct way to define a handle class in MATLAB?

easy

A. classdef MyClass < handle
properties
Value
end
end

B. classdef MyClass
properties
Value
end
end

C. classdef MyClass < value
properties
Value
end
end

D. classdef MyClass < shared
properties
Value
end
end

Solution

1. Step 1: Identify handle class syntax

   In MATLAB, to create a handle class, the class must inherit from the built-in handle class using < syntax.

2. Step 2: Check options for correct inheritance

   classdef MyClass < handle properties Value end end correctly inherits from handle. Options A, B, and D either omit inheritance or use invalid base classes.

3. Final Answer:

   classdef MyClass < handle properties Value end end -> Option A

4. Quick Check:

   Handle class inherits from 'handle' keyword [OK]

Hint: Handle classes inherit from 'handle' keyword in classdef [OK]

Common Mistakes:

• Omitting '< handle' in class definition
• Using incorrect base class names
• Confusing handle with value class syntax

3. Consider the following MATLAB code:

classdef MyHandleClass < handle
    properties
        Data
    end
end

obj1 = MyHandleClass();
obj1.Data = 10;
obj2 = obj1;
obj2.Data = 20;
disp(obj1.Data);

What is the output?

medium

A. 10

B. 20

C. Error: Cannot assign obj2 to obj1

D. Empty output

Solution

1. Step 1: Understand handle class assignment

   Since MyHandleClass inherits from handle, obj2 = obj1 makes obj2 reference the same object as obj1.

2. Step 2: Trace property change effect

   Changing obj2.Data to 20 changes the shared object, so obj1.Data also becomes 20.

3. Final Answer:

   20 -> Option B

4. Quick Check:

   Handle class copies share data, so output is 20 [OK]

Hint: Handle class copies share data; changes reflect everywhere [OK]

Common Mistakes:

• Thinking obj1.Data remains 10 after obj2.Data change
• Expecting error on assignment
• Confusing handle with value class behavior

4. The following MATLAB code is intended to create two independent objects, but it does not. What is the error?

classdef MyValueClass < handle
    properties
        Data
    end
end

obj1 = MyValueClass();
obj1.Data = 5;
obj2 = obj1;
obj2.Data = 10;
disp(obj1.Data);

medium

A. MyValueClass should inherit from handle to share data.

B. MyValueClass should inherit from handle to create independent copies.

C. MyValueClass should inherit from handle to avoid independent copies.

D. MyValueClass should not inherit from handle to keep copies independent.

Solution

1. Step 1: Analyze class inheritance

   The class MyValueClass inherits from handle, making it a handle class that shares data between copies.

2. Step 2: Check object assignment behavior

   obj2 = obj1 references the same object. Changing obj2.Data affects obj1.Data, so copies are not independent.

3. Step 3: Identify the error

   To create independent copies, it should be a value class by not inheriting from handle.

4. Final Answer:

   MyValueClass should not inherit from handle to keep copies independent. -> Option D

5. Quick Check:

   Value classes = independent copies, no handle inheritance [OK]

Hint: Value classes must NOT inherit handle to keep copies independent [OK]

Common Mistakes:

• Thinking value classes must inherit handle
• Confusing inheritance effect on copy behavior
• Assuming handle inheritance creates independent copies

5. You want to design a MATLAB class to represent a shared configuration object that multiple parts of your program can modify and see updates immediately. Which class type should you choose and why?

hard

A. Use a value class, because copies keep data separate and avoid unintended side effects.

B. Use a value class, because it allows shared data between copies automatically.

C. Use a handle class, because copies share the same data and reflect changes immediately.

D. Use a handle class, because it creates independent copies that do not affect each other.

Solution

1. Step 1: Understand the requirement for shared updates

   The program needs a shared configuration object where changes by one part are seen by others immediately.

2. Step 2: Match requirement to class behavior

   Handle classes share data between copies, so changes to one copy affect all references. Value classes keep data separate, so changes do not propagate.

3. Final Answer:

   Use a handle class, because copies share the same data and reflect changes immediately. -> Option C

4. Quick Check:

   Shared updates need handle class [OK]

Hint: Shared data needs handle class for immediate update reflection [OK]

Common Mistakes:

• Choosing value class for shared data
• Misunderstanding copy behavior of handle classes
• Assuming value classes share data automatically