Developers from Facebook have released a new version of HHVM, the Hip Hop Virtual Machine. The PHP support in new release has been changed to default to PHP 7 rather than the PHP 5 of the previous version.

HHVM is an open-source virtual machine designed for executing programs written in Hack and PHP.  It was developed at Facebook to provide a way to convert PHP script to C++ so it could be compiled and run on web servers. HHVM supports Hack and PHP 7. PHP 5 is still available, but unsupported. HHVM uses just-in-time (JIT) compilation to combine good performance with a flexible development environment. 

Hack is a programming language developed by Facebook for HHVM. It is designed to combine the fast development cycle of a dynamically typed language with the discipline provided by static typing. It does this by offering 'instantaneous type checking'. This is achieved by Hack incrementally checking your files as you edit them. The check typically runs in less than 200 milliseconds, so is an acceptable overhead. Facebook has moved its entire codebase across to Hack, and there is an open source version complete with HHVM.

The PHP 7 support in the new version goes beyond it being the default, with more extensive support for PHP 7 features. Visibility modifiers on constants no longer cause a parsing error, though they are still ignored. Several more kinds of expressions are now permitted as callable. The expressions were already understood by the Hack typechecker, but not supported by the runtime. Another PHP 7 compatibility improvement is support for the PHP7 Throwable, Error and Exception hierarchy, including in Hack and in PHP5 mode.

Away from PHP 7, support has been added for the Visual Studio Code Debug Adapter Protocol in addition to hphpd and XDebug. The VS protocol is now the recommended debug interface. Another improvement fixes a CVE security problem that could potentially cause a denial of service issue from the Proxygen handling of invalid HTTP2 settings which can cause the server to spend disproportionate resource. Elsewhere, Hack inout function parameters are now supported, and a number of other improvements have been made to Hack.
 

More Information

HHVM Site

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