Refactoring is the process of restructuring existing computer code without changing its external behavior. It aims to improve the nonfunctional attributes of the software. Refactoring can help make code more readable, maintainable, and scalable. In this section, we will explore various refactoring techniques in Delphi/Object Pascal.
Key Concepts of Refactoring
- Code Smells: Indicators that there might be a problem in the code.
- Refactoring Patterns: Common solutions to recurring design problems.
- Automated Refactoring Tools: Tools that help automate the refactoring process.
Common Code Smells
- Duplicated Code: Same code structure repeated in multiple places.
- Long Methods: Methods that are too long and do too much.
- Large Classes: Classes that have too many responsibilities.
- Long Parameter Lists: Methods that take too many parameters.
- Divergent Change: When one class is commonly changed in different ways for different reasons.
- Shotgun Surgery: When a single change requires many small changes to multiple classes.
Refactoring Patterns
- Extract Method
Problem: A method is too long or does too many things.
Solution: Break the method into smaller, more focused methods.
Example:
procedure ProcessOrder(Order: TOrder);
begin
// Validate order
if not ValidateOrder(Order) then
Exit;
// Calculate total
Order.Total := CalculateTotal(Order);
// Save order to database
SaveOrder(Order);
end;
function ValidateOrder(Order: TOrder): Boolean;
begin
// Validation logic here
end;
function CalculateTotal(Order: TOrder): Currency;
begin
// Calculation logic here
end;
procedure SaveOrder(Order: TOrder);
begin
// Database save logic here
end;
- Rename Method
Problem: A method name does not clearly describe its purpose.
Solution: Rename the method to better reflect its functionality.
Example:
- Move Method
Problem: A method is more related to another class than the one it currently resides in.
Solution: Move the method to the more appropriate class.
Example:
// Before
type
TOrder = class
procedure PrintOrder;
end;
// After
type
TOrderPrinter = class
procedure PrintOrder(Order: TOrder);
end;
- Inline Method
Problem: A method is too simple and does not justify its existence.
Solution: Replace the method call with the method's content.
Example:
// Before function GetDiscount: Double; begin Result := 0.1; end; Total := Price * (1 - GetDiscount); // After Total := Price * 0.9;
- Replace Magic Numbers with Constants
Problem: Using hard-coded numbers in the code.
Solution: Replace them with named constants.
Example:
// Before Total := Price * 0.9; // After const DISCOUNT_RATE = 0.1; begin Total := Price * (1 - DISCOUNT_RATE); end;
Practical Exercise
Exercise 1: Refactor a Long Method
Task: Refactor the following method by extracting smaller methods.
procedure ProcessCustomerOrder(Customer: TCustomer; Order: TOrder);
begin
// Validate customer
if Customer.IsValid then
begin
// Calculate order total
Order.Total := 0;
for Item in Order.Items do
begin
Order.Total := Order.Total + Item.Price;
end;
// Apply discount
if Customer.IsPremium then
begin
Order.Total := Order.Total * 0.9;
end;
// Save order
SaveOrderToDatabase(Order);
end;
end;Solution:
procedure ProcessCustomerOrder(Customer: TCustomer; Order: TOrder);
begin
if not ValidateCustomer(Customer) then
Exit;
CalculateOrderTotal(Order);
ApplyDiscountIfPremium(Customer, Order);
SaveOrderToDatabase(Order);
end;
function ValidateCustomer(Customer: TCustomer): Boolean;
begin
Result := Customer.IsValid;
end;
procedure CalculateOrderTotal(Order: TOrder);
var
Item: TOrderItem;
begin
Order.Total := 0;
for Item in Order.Items do
begin
Order.Total := Order.Total + Item.Price;
end;
end;
procedure ApplyDiscountIfPremium(Customer: TCustomer; Order: TOrder);
begin
if Customer.IsPremium then
begin
Order.Total := Order.Total * 0.9;
end;
end;Summary
In this section, we covered the importance of refactoring and various techniques to improve code quality. We discussed common code smells and refactoring patterns such as Extract Method, Rename Method, Move Method, Inline Method, and Replace Magic Numbers with Constants. By applying these techniques, you can make your Delphi/Object Pascal code more readable, maintainable, and scalable.
Next, we will delve into Unit Testing and Test-Driven Development to ensure that our refactored code remains functional and reliable.
Delphi/Object Pascal Programming Course
Module 1: Introduction to Delphi/Object Pascal
- Introduction to Delphi and Object Pascal
- Setting Up the Development Environment
- First Delphi Application
- Basic Syntax and Structure
- Variables and Data Types
Module 2: Control Structures and Procedures
- Conditional Statements
- Loops and Iteration
- Procedures and Functions
- Scope and Lifetime of Variables
- Error Handling and Debugging
Module 3: Working with Data
Module 4: Object-Oriented Programming
- Introduction to OOP
- Classes and Objects
- Inheritance and Polymorphism
- Interfaces and Abstract Classes
- Exception Handling in OOP
Module 5: Advanced Delphi Features
- Generics and Collections
- Multithreading and Parallel Programming
- Component-Based Development
- Delphi Runtime Library (RTL)
- Advanced Debugging Techniques
Module 6: GUI Development with VCL and FMX
- Introduction to VCL
- Creating Forms and Controls
- Event-Driven Programming
- Introduction to FireMonkey (FMX)
- Cross-Platform Development with FMX
Module 7: Web and Mobile Development
- Web Development with Delphi
- RESTful Services
- Mobile Development with Delphi
- Deploying Mobile Applications
- Integrating with Web Services
Module 8: Best Practices and Design Patterns
- Code Organization and Documentation
- Design Patterns in Delphi
- Refactoring Techniques
- Unit Testing and Test-Driven Development
- Performance Optimization