简介
组合模式又叫对象树，将对象按照树形结构串起来，呈现出局部和整体相同的特性。
树中每个节点都由两部分组成，首先节点有自己的业务数据，其次节点内可以含有子节点集合。
比如盒子中可以放物品，也可以放其他小盒子，小盒子里又可以放物品和其他更小的盒子。
当计算盒子的物品价格时，只需要将盒子里本身的物品价格，加上小盒子里所有物品价格即可，递归处理。
类图
角色
或者也可以不区分是否是叶子节点，都视为节点即可
类图
图中显示，Leaf 和 Composite 都实现 Component 接口。
Composite 可添加或删除子节点，execute 则指派调用子节点的 execute 方法。
Leaf 的 execute 是真正执行逻辑的地方
类图
代码
<?php
abstract class Component{ protected $parent;
public function setParent(Component $parent) { $this->parent = $parent; }
public function getParent(): Component { return $this->parent; }
public function add(Component $component): void { }
public function remove(Component $component): void { }
public function isComposite(): bool { return false; }
abstract public function operation(): string;}
class Leaf extends Component{ public function operation(): string { return "Leaf"; }}
class Composite extends Component{ protected $children;
public function __construct() { $this->children = new \SplObjectStorage(); }
public function add(Component $component): void { $this->children->attach($component); $component->setParent($this); }
public function remove(Component $component): void { $this->children->detach($component); $component->setParent(null); }
public function isComposite(): bool { return true; }
public function operation(): string { $results = []; foreach ($this->children as $child) { $results[] = $child->operation(); }
return "Branch(" . implode("+", $results) . ")"; }}
function clientCode(Component $component){ echo "RESULT: " . $component->operation();}
// 只有一个叶子节点$simple = new Leaf();echo "Client: I've got a simple component:\n";clientCode($simple);
echo "\n";
// 构建一个tree$tree = new Composite();$branch1 = new Composite();$branch1->add(new Leaf());$branch1->add(new Leaf());$branch2 = new Composite();$branch2->add(new Leaf());$tree->add($branch1);$tree->add($branch2);echo "Client: Now I've got a composite tree:\n";clientCode($tree);
// 合并两个treefunction clientCode2(Component $component1, Component $component2){ if ($component1->isComposite()) { $component1->add($component2); } echo "RESULT: " . $component1->operation();}
echo "\n";echo "Client: I don't need to check the components classes even when managing the tree:\n";clientCode2($tree, $simple);
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output:
Client: I've got a simple component:RESULT: LeafClient: Now I've got a composite tree:RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf))Client: I don't need to check the components classes even when managing the tree:RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf)+Leaf)
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