Анонимная функция и замыкание

$logdb = function ($string) { Logger::log('debug','database',$string); };
$logdb('Connected to database'); 
$logdb('Insert Hammer into to parts table');

$string = "asdf";
$logdb = function () use ($string)
    {
        Logger::log('debug','database',$string);
    };
$logdb('Connected to database'); 
$logdb('Insert Hammer into to parts table');

function test()
{
    static $a = 1;
    return $a++;
}
 
echo test(), PHP_EOL;
echo test();

$a = 1;
$b = function () use(&$a)
{
    echo $a++.PHP_EOL;
};
$b();
$b();
$b();

$a = 1;
$b = function (&$a)
{
    echo $a++.PHP_EOL;
};
$b($a);
$b($a);
$b($a);

$arExclude = array(1, 3, 5);
 
$arOutput = array_filter($arInput, function ($value) use($arExclude) {
   return $value > 10 && ! in_array($value, $arExclude);
});

function getValute($name)
{
    return function ($name) use (&$xml) {
        if (!isset($xml)) {
            $file = 'http://pfsoft.com.ua/service/currency/?date=' . date('dmY');
            $xml = simplexml_load_file($file);
        }
        $valute = $xml->xpath("/ValCurs/Valute[CharCode='$name']")[0];
        return $valute->Nominal . ' ' . $valute->Name . ' - ' . $valute->Value;
    };
}
 
$valute = getValute($name);
echo $valute('USD'), '<br>', $valute('EUR');

function diffTime()
{
    return function()use(&$time){
        if(isset($time)){
            echo (microtime(true)- $time), PHP_EOL;
            $time = null;
        }else{
            $time = microtime(true);
        }
    };
}
$test = diffTime();
$test();
sleep(1);
$test();
$test();
sleep(2);
$test();

function sum()
{
    return function ($a) {
        echo $a + 1;
    };
}
 
$test = sum();
$test(1);