Magento 2 : print_r or var_dump is not working

print_r and var_dump does not play well when there are a lot of object involved.
Both of them try to print the category object and this object has a lot of objects attached to it because of the dependency injection

If you take a look at the constructor from the category model you will see this:

public function __construct(
    MagentoFrameworkModelContext $context,
    MagentoFrameworkRegistry $registry,
    MagentoFrameworkApiExtensionAttributesFactory $extensionFactory,
    AttributeValueFactory $customAttributeFactory,
    MagentoStoreModelStoreManagerInterface $storeManager,
    MagentoCatalogApiCategoryAttributeRepositoryInterface $metadataService,
    MagentoCatalogModelResourceModelCategoryTree $categoryTreeResource,
    MagentoCatalogModelResourceModelCategoryTreeFactory $categoryTreeFactory,
    MagentoStoreModelResourceModelStoreCollectionFactory $storeCollectionFactory,
    MagentoFrameworkUrlInterface $url,
    MagentoCatalogModelResourceModelProductCollectionFactory $productCollectionFactory,
    MagentoCatalogModelConfig $catalogConfig,
    MagentoFrameworkFilterFilterManager $filter,
    IndexerCategoryFlatState $flatState,
    MagentoCatalogUrlRewriteModelCategoryUrlPathGenerator $categoryUrlPathGenerator,
    UrlFinderInterface $urlFinder,
    MagentoFrameworkIndexerIndexerRegistry $indexerRegistry,
    CategoryRepositoryInterface $categoryRepository,
    MagentoFrameworkModelResourceModelAbstractResource $resource = null,
    MagentoFrameworkDataCollectionAbstractDb $resourceCollection = null,
    array $data = []
) {
    $this->metadataService = $metadataService;
    $this->_treeModel = $categoryTreeResource;
    $this->_categoryTreeFactory = $categoryTreeFactory;
    $this->_storeCollectionFactory = $storeCollectionFactory;
    $this->_url = $url;
    $this->_productCollectionFactory = $productCollectionFactory;
    $this->_catalogConfig = $catalogConfig;
    $this->filter = $filter;
    $this->flatState = $flatState;
    $this->categoryUrlPathGenerator = $categoryUrlPathGenerator;
    $this->urlFinder = $urlFinder;
    $this->indexerRegistry = $indexerRegistry;
    $this->categoryRepository = $categoryRepository;
    parent::__construct(
        $context,
        $registry,
        $extensionFactory,
        $customAttributeFactory,
        $storeManager,
        $resource,
        $resourceCollection,
        $data
    );
}

Each object passed to the constructor is referenced in the category model.
And each object may have additional objects linked to it.
In conclusion print_r and var_dump won't work for most of the objects in Magento 2.
Solutions:

• use xdebug to see how the object looks like.
• print only $category->getData() to see the actual properties of the category object (but this might not always work either).