Builder.md

Builder Pattern

• The builder pattern is a design pattern designed to provide a flexible solution to various object creation problems in object-oriented programming.
• The intent of the Builder design pattern is to separate the construction of a complex object from its representation.
• By doing so, the same construction process can create different representations.

Structure

• It consists of builder, concrete builder, director and product.
• Builder: An abstract class that will contain the methods for building the product.
• Concrete Builder: A class that will implement the Builder and will be responsible for building the product.
• Director: A class that will use the Builder interface for building the product.
• Product: A class that will contain the actual implementation of the product.

Example

// Builder class
class AdditionBuilder : Builder<decimal>
{
    private decimal num;

    public override decimal Output() => num;

    protected override void Build(decimal input) => num = decimal.Add(num, input);

// Pattern execution
var builder = new AdditionBuilder();
builder.Append(1.2m).Append(2.4m).Append(3.6m);
Console.WriteLine($"Output: {builder.Output()}");

// Output
Output: 7.2

Classes and interfaces used in example:

• IBuilder
• Builder

Benefits

• The parameters to the constructor are reduced and are provided in highly readable method calls.
• Object is always instantiated in a complete state.
• The builder pattern helps to avoid the inconsistent state problem.

Similarity with other patterns

• Builder pattern is similar to the Abstract Factory pattern in that, both create complex objects.
• The difference is that the Builder pattern focuses on constructing a complex object step by step whereas the Abstract Factory pattern focuses on families of related objects.
• The Builder pattern returns the product as a final step, but as far as the Abstract Factory pattern is concerned, the product gets returned immediately.