11. 享元模式（Flyweight）

问题：大量相似对象占用过多内存。

核心：把不变的部分（内在状态）共享，可变的部分（外在状态）外部传入。

class TextStyle {
  constructor(font, size, color) {
    this.font = font;
    this.size = size;
    this.color = color;
  }
}

class StyleFactory {
  #cache = new Map();
  getStyle(font, size, color) {
    const key = `${font}-${size}-${color}`;
    if (!this.#cache.has(key)) {
      this.#cache.set(key, new TextStyle(font, size, color));
    }
    return this.#cache.get(key);
  }
}

const factory = new StyleFactory();
const s1 = factory.getStyle('Arial', 14, 'black');
const s2 = factory.getStyle('Arial', 14, 'black');
console.log(s1 === s2); // true — 共享同一个对象

package flyweight

import "fmt"

type TextStyle struct {
  Font  string
  Size  int
  Color string
}

type StyleFactory struct {
  cache map[string]*TextStyle
}

func NewStyleFactory() *StyleFactory {
  return &StyleFactory{cache: make(map[string]*TextStyle)}
}

func (f *StyleFactory) GetStyle(font string, size int, color string) *TextStyle {
  key := fmt.Sprintf("%s-%d-%s", font, size, color)
  if _, ok := f.cache[key]; !ok {
    f.cache[key] = &TextStyle{Font: font, Size: size, Color: color}
  }
  return f.cache[key]
}