此扩展是实验性 的。 此扩展的表象，包括其函数名称以及其他此扩展的相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本扩展风险自担 。
This extension allows the loading of shared libraries (.DLL or .so), calling of C functions and accessing of C data structures in pure PHP, without having to have deep knowledge of the Zend extension API, and without having to learn a third “intermediate” language. The public API is implemented as a single class FFI with several static methods (some of them may be called dynamically), and overloaded object methods, which perform the actual interaction with C data.
FFI is dangerous, since it allows to interface with the system on a very low level. The FFI extension should only be used by developers having a working knowledge of C and the used C APIs. To minimize the risk, the FFI API usage may be restricted with the ffi.enable php.ini directive.
The FFI extension does not render the classic PHP extension API obsolete; it is merely provided for ad-hoc interfacing with C functions and data structures.
Currently, accessing FFI data structures is significantly (about 2 times) slower than accessing native PHP arrays and objects. Therefore, it makes no sense to use the FFI extension for speed; however, it may make sense to use it to reduce memory consumption.