phpの@(アットマーク)はオーバーヘッドが大きいから使わないほうがよい

<?php
// 1.
if (isset($checkedAry['key']) && $checkedAry['key'] == "val") {
    // 処理
}

// 2. 1より早いんじゃね？
if ($checkedAry['key'] == "val") {
    // でもNoticeでちゃうよ！
    // PHP Notice:  Undefined index: index
}

// 3. 2の「PHP Notice」の回避策　＠
if (@$checkedAry['key'] == "val") {
    // 処理
}

<?php
$ary = array(
    array( "key1" => "val1", "key2" => "val2","key3" => "val3","key4" => "val4"),
    array( "key1" => "val1", "key2" => "val2","key3" => "val3"),
);

$time_start = microtime(true);

$index = 0;
foreach (range(1,100000) as $count) {
    $index = 1 - $index;
    $checkedAry = $ary[$index];
    if (isset($checkedAry['key4']) && $checkedAry['key4'] == "val4") {
        pow($count, $count);
    }
}

$time = microtime(true) - $time_start;
echo "$time second";

$time_start = microtime(true);

$index = 0;
foreach (range(1,100000) as $count) {
    $index = 1 - $index;
    $checkedAry = $ary[$index];
    if (@$checkedAry['key4'] == "val4") {
        pow($count, $count);
    }
}

$time = microtime(true) - $time_start;
echo "$time second";