Since PHP6 was never fully developed, PHP7’s release signaled the end of PHP5 and simultaneously rung in the sixth installment of the programming language. The scripting language itself changed little with the release, which is why PHP7 largely remains downwardly compatible. This feature allows almost all applications, even those designed for previous versions, to run on PHP7. Compatibility issues may still arise when dealing with older extensions that no longer receive regular updates. The best example for this is the old extension for accessing MySQL databases that is no longer supported in version 7. Switching to the better MySQLi extension or the comparable PDO (PHP Data Objects), is therefore recommended in such cases.
Perhaps the most attractive new feature of PHP7 is its performance boost, which enables developers to better optimize the core of PHP. In addition to the improved speed (PHP7 is about twice as fast as its predecessor), the new version also takes up less working memory. Not only has the execution of the compiled bytecode been completely renovated, but other core components have also seen fundamental changes, including the parser, lexer, and bytecode generator. Instead of drafting code directly out of the parser, PHP7 creates an abstract syntax tree that establishes the basis for generating bytecode commands.
Another feature is that users are now able to define scalar data types - data types that only store one single value – and return types in the program code. In this way, PHP is extended by the integer, Boolean, float, and string types.