[TOC] # php 7 优化和不兼容 ~~~ $goo = [ "bar" => [ "baz" => 100, "cug" => 900 ] ]; $foo = "goo"; $$foo["bar"]["baz"]; // 实际为：($$foo)['bar']['baz']; PHP 5 中为：${$foo['bar']['baz']};https://zhuanlan.zhihu.com/p/29478077 https://github.com/justcodingnobb/fuck-php-interview https://github.com/todayqq/caseInterviewQuestions $fn = function (?int $in) { return $in ?? "NULL"; }; $fn(null); $fn(5); $fn(); // TypeError: Too few arguments to function {closure}() ~~~ # php升级优化不兼容