ClassName-类名
getIdByMail-方法名
$a_b 变量名
Internally, PHP itself uses Underscores for variables and functions, camelCase for Methods, and PascalCase for Classes, as stated in this PHP documentation page (userlandnaming.rules), and as spelled out in this PHP coding standards document. That said, various frameworks follow different conventions of their own. – SherylHohman Apr 6 at 18:11