- array_map: documentation ( source)
- var_dump: documentation ( source)
- implode: documentation ( source)
- array_keys: documentation ( source)
<?php
$fields = [
'email' => '',
'gender' => '',
'birthday' => '',
'name' => '',
'country_code' => '',
'city' => '',
'photo' => '',
'created_at' => '',
'project' => '',
];
echo implode(',',array_map(function($f){return ':'.$f;}, array_keys($fields)));
var_dump($fields);