Builder

The Builder Pattern is a creational design pattern that provides a flexible solution for constructing complex objects step by step. It allows you to create different representations of an object using the same construction process.

Problem Statement

• When creating an object involves multiple steps or parameters, managing the construction process can become cumbersome.
• You want to avoid a "telescoping constructor" problem (where constructors take many parameters) and ensure that your object is immutable after creation.

Benefits of the Builder Pattern

• Flexibility: Easily construct different representations of an object.
• Readability: Method chaining makes the construction process clear and concise.
• Encapsulation: The construction logic is encapsulated within the builder, separating it from the client code.

Real-World Example

Consider building a computer. A computer can have various components like CPU, RAM, storage, etc.

Instead of requiring all these parameters in a constructor, the builder pattern allows you to set each component step by step.

Implementation

package main

import "fmt"

// Product
type Computer struct {
    CPU     string
    RAM     string
    Storage string
    OS      string
}

// Builder Interface
type ComputerBuilder interface {
    SetCPU(cpu string) ComputerBuilder
    SetRAM(ram string) ComputerBuilder
    SetStorage(storage string) ComputerBuilder
    SetOS(os string) ComputerBuilder
    Build() *Computer
}

// Concrete Builder
type PCBuilder struct {
    computer *Computer
}

func NewPCBuilder() *PCBuilder {
    return &PCBuilder{&Computer{}}
}

func (b *PCBuilder) SetCPU(cpu string) ComputerBuilder {
    b.computer.CPU = cpu
    return b
}

func (b *PCBuilder) SetRAM(ram string) ComputerBuilder {
    b.computer.RAM = ram
    return b
}

func (b *PCBuilder) SetStorage(storage string) ComputerBuilder {
    b.computer.Storage = storage
    return b
}

func (b *PCBuilder) SetOS(os string) ComputerBuilder {
    b.computer.OS = os
    return b
}

func (b *PCBuilder) Build() *Computer {
    return b.computer
}

// Client Code
func main() {
    builder := NewPCBuilder()

    computer := builder.
        SetCPU("Intel i7").
        SetRAM("16GB").
        SetStorage("1TB SSD").
        SetOS("Windows 7").
        Build()

    fmt.Printf("Computer built: %+v\n", computer)
}

Product (Computer): Represents the complex object that will be built with various attributes.

Builder Interface (ComputerBuilder): Defines methods for setting each component of the product.

Concrete Builder (PCBuilder): Implements the builder interface.

• Provides methods to set CPU, RAM, Storage, and OS, returning the builder itself for method chaining.
• The Build() method returns the final Computer object.

Client Code: Creates a new builder instance.

• Configures the computer step by step using method chaining.
• Calls Build() to retrieve the final product.