//  驼峰 转 _小写 fooBar => foo_bar
function upToLow($low){
    return preg_replace_callback('/([A-Z])/',function($matches){
//        print_r($matches); //Array ( [0] => _b [1] => b )
        return '_'.strtolower($matches[1]);
    },$low);
}
// _小写 转 驼峰 foo_bar_b => fooBarB
function lowToUp($low){
    return preg_replace_callback('/_+([a-z])/',function($matches){
        return strtoupper($matches[1]);
    },$low);
}
//批量转 _小写 转 驼峰
function arrLowToUp($a){
    $w = [];
    foreach($a as $k=>$v){
        $cg = lowToUp($k);
        $w[$cg]= $v;
    }
    return $w;
}
//批量转 _小写 转 驼峰
function arrUpToLow($a){
    $w = [];
    foreach($a as $k=>$v){
        $cg = upToLow($k);
        $w[$cg]= $v;
    }
    return $w;
}