What problem does the Builder pattern solve? Show an example.

class PizzaBuilder:
    def __init__(self):
        self.size, self.toppings = "medium", []

    def large(self):
        self.size = "large"
        return self  # returning self allows chaining

    def topping(self, name):
        self.toppings.append(name)
        return self

    def build(self):
        if len(self.toppings) > 3:
            raise ValueError("max 3 toppings")
        return f"{self.size} pizza with {', '.join(self.toppings) or 'cheese'}"


print(PizzaBuilder().large().topping("olives").topping("basil").build())
print(PizzaBuilder().build())

class PizzaBuilder {
  private size = "medium";
  private toppings: string[] = [];

  large(): this { this.size = "large"; return this; } // returning this allows chaining
  topping(name: string): this { this.toppings.push(name); return this; }

  build(): string {
    if (this.toppings.length > 3) throw new Error("max 3 toppings");
    return `${this.size} pizza with ${this.toppings.join(", ") || "cheese"}`;
  }
}

console.log(new PizzaBuilder().large().topping("olives").topping("basil").build());
console.log(new PizzaBuilder().build());

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        System.out.println(new PizzaBuilder().large().topping("olives").topping("basil").build());
        System.out.println(new PizzaBuilder().build());
    }
}

class PizzaBuilder {
    private String size = "medium";
    private final List<String> toppings = new ArrayList<>();

    PizzaBuilder large() { size = "large"; return this; } // returning this allows chaining
    PizzaBuilder topping(String name) { toppings.add(name); return this; }

    String build() {
        if (toppings.size() > 3) throw new IllegalStateException("max 3 toppings");
        return size + " pizza with " + (toppings.isEmpty() ? "cheese" : String.join(", ", toppings));
    }
}

<?php
class PizzaBuilder {
    private string $size = "medium";
    private array $toppings = [];

    public function large(): static { $this->size = "large"; return $this; } // returning $this allows chaining
    public function topping(string $name): static { $this->toppings[] = $name; return $this; }

    public function build(): string {
        if (count($this->toppings) > 3) throw new LogicException("max 3 toppings");
        return "{$this->size} pizza with " . (implode(", ", $this->toppings) ?: "cheese");
    }
}

echo (new PizzaBuilder())->large()->topping("olives")->topping("basil")->build(), "\n";
echo (new PizzaBuilder())->build(), "\n";