Sometime its needed to store some calculations for later use in the same php request. TYPO3 has cache for that that by default uses memory as backend.

$runtimeCache = GeneralUtility::makeInstance(CacheManager::class)->getCache('cache_runtime');
$runtimeCacheIdentifier = 'foo-bar';
$runtimeCache->set($runtimeCacheIdentifier, 1000);
$test = $runtimeCache->get($runtimeCacheIdentifier);