Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
| 1 | <?php  | 
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| 29 | class StockDiffProcessor extends ItemHolderValidator implements PurchaseProcessor  | 
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| 30 | { | 
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| 31 | /**  | 
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| 32 | * @var ProductClassRepository  | 
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| 33 | */  | 
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| 34 | protected $productClassRepository;  | 
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| 35 | |||
| 36 | /**  | 
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| 37 | * StockProcessor constructor.  | 
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| 38 | *  | 
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| 39 | * @param ProductClassRepository $productClassRepository  | 
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| 40 | */  | 
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| 41 | 713 | public function __construct(ProductClassRepository $productClassRepository)  | 
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| 45 | |||
| 46 | /**  | 
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| 47 | * @param ItemHolderInterface $itemHolder  | 
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| 48 | * @param PurchaseContext $context  | 
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| 49 | *  | 
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| 50 | * @throws \Eccube\Service\PurchaseFlow\InvalidItemException  | 
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| 51 | */  | 
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| 52 | 156 | public function validate(ItemHolderInterface $itemHolder, PurchaseContext $context)  | 
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| 53 |     { | 
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| 54 | 156 |         if (is_null($context->getOriginHolder())) { | 
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| 55 | return;  | 
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| 56 | }  | 
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| 57 | |||
| 58 | 156 | $From = $context->getOriginHolder();  | 
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| 59 | 156 | $To = $itemHolder;  | 
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| 60 | 156 | $diff = $this->getDiffOfQuantities($From, $To);  | 
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| 61 | |||
| 62 | 156 |         foreach ($diff as $id => $quantity) { | 
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| 63 | /** @var ProductClass $ProductClass */  | 
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| 64 | 156 | $ProductClass = $this->productClassRepository->find($id);  | 
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| 65 | 156 |             if ($ProductClass->isStockUnlimited()) { | 
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| 66 | continue;  | 
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| 67 | }  | 
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| 68 | 156 | ||
| 69 | $stock = $ProductClass->getStock();  | 
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| 70 | 156 | $Items = $To->getProductOrderItems();  | 
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| 71 |             $Items = array_filter($Items, function ($Item) use ($id) { | 
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| 72 | return $Item->getProductClass()->getId() == $id;  | 
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| 73 | });  | 
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| 74 |             $toQuantity = array_reduce($Items, function ($quantity, $Item) { | 
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| 75 | return $quantity += $Item->getQuantity();  | 
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| 76 | }, 0);  | 
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| 77 | |||
| 78 | // ステータスをキャンセルに変更した場合  | 
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| 79 | if ($To->getOrderStatus() && $To->getOrderStatus()->getId() == OrderStatus::CANCEL  | 
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| 80 |                 && $From->getOrderStatus() && $From->getOrderStatus()->getId() != OrderStatus::CANCEL) { | 
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| 81 | View Code Duplication |                 if ($stock + $toQuantity < 0) { | 
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| 82 | 156 |                     $this->throwInvalidItemException(trans('purchase_flow.over_stock', ['%name%' => $ProductClass->formattedProductName()])); | 
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| 83 | 156 | }  | 
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| 84 | // ステータスをキャンセルから対応中に変更した場合  | 
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| 85 | } elseif ($To->getOrderStatus() && $To->getOrderStatus()->getId() == OrderStatus::IN_PROGRESS  | 
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| 86 |                 && $From->getOrderStatus() && $From->getOrderStatus()->getId() == OrderStatus::CANCEL) { | 
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| 87 | View Code Duplication |                 if ($stock - $toQuantity < 0) { | 
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| 88 |                     $this->throwInvalidItemException(trans('purchase_flow.over_stock', ['%name%' => $ProductClass->formattedProductName()])); | 
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| 89 | 156 | }  | 
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| 90 | View Code Duplication |             } else { | 
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| 91 | 156 |                 if ($stock - $quantity < 0) { | 
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| 92 | 156 |                     $this->throwInvalidItemException(trans('purchase_flow.over_stock', ['%name%' => $ProductClass->formattedProductName()])); | 
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| 93 | 156 | }  | 
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| 94 | }  | 
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| 95 | 156 | }  | 
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| 96 | 156 | }  | 
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| 97 | |||
| 98 | 156 | protected function getDiffOfQuantities(ItemHolderInterface $From, ItemHolderInterface $To)  | 
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| 124 | |||
| 125 | 156 | protected function getQuantityByProductClass(ItemHolderInterface $ItemHolder)  | 
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| 141 | 5 | ||
| 142 | /**  | 
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| 143 | 5 | * 受注の仮確定処理を行います。  | 
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| 144 | *  | 
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| 145 | * @param ItemHolderInterface $target  | 
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| 146 | * @param PurchaseContext $context  | 
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| 147 | 5 | *  | 
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| 148 | * @throws PurchaseException  | 
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| 149 | 5 | */  | 
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| 150 | public function prepare(ItemHolderInterface $target, PurchaseContext $context)  | 
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| 176 | 5 | ||
| 177 | /**  | 
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| 178 | * 受注の確定処理を行います。  | 
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| 179 | 5 | *  | 
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| 180 | * @param ItemHolderInterface $target  | 
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| 181 | * @param PurchaseContext $context  | 
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| 182 | *  | 
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| 183 | * @throws PurchaseException  | 
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| 184 | */  | 
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| 185 | public function commit(ItemHolderInterface $target, PurchaseContext $context)  | 
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| 190 | |||
| 191 | /**  | 
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| 192 | * 仮確定した受注データの取り消し処理を行います。  | 
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| 193 | *  | 
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| 194 | * @param ItemHolderInterface $itemHolder  | 
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| 195 | * @param PurchaseContext $context  | 
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| 196 | */  | 
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| 197 | public function rollback(ItemHolderInterface $itemHolder, PurchaseContext $context)  | 
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| 202 | }  | 
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| 203 | 
Let’s take a look at an example:
In the above example, the authenticate() method works fine as long as you just pass instances of MyUser. However, if you now also want to pass a different implementation of User which does not have a getDisplayName() method, the code will break.
Available Fixes
Change the type-hint for the parameter:
Add an additional type-check:
Add the method to the interface: