- var_dump: documentation ( source)
- debug_backtrace: documentation ( source)
<?php
function userland_func_num_args() { return count(debug_backtrace()[1]['args'][$idx]); }
function foo() { return func_num_args(); }
function bar() { return userland_func_num_args(); }
var_dump(foo('foo', 'bar'));
var_dump(bar('foo', 'bar'));