The HipHop Virtual Machine (HHVM) is an alternative PHP runtime implementation. It executes scripts JIT-compiled for higher performance, but retains most dynamic features, weak typing, and scripting language capabilities. While its companion language "Hack" constraints some features for additional execution speed. HHVM is developed and used by Facebook, where it achieved significant performance gains and reduced memory consumptiom. Its syntax and standard library feature set is meanwhile compat
major feature: Core changes: Performance improvements for certain usages of strtr(). Fixes to rand() when requesting very large integers. XDebug compatibility and resource usage fixes. Improved reflection support. The usual myriad of bug fixes and general performance improvements. Hack language: Dramatically improved type inference for arrays. Improved typechecking for some standard library functions. Other minor fixes, e.g., improved type enforcement in some edge cases and fixes to using shapes inside namespaced code.