【PHP】三元運算子 ?: 問號冒號

動機

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記性不好，寫一遍筆記比較記得起來

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解決方案

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1. $param = isset($_GET['param']) ? $_GET['param'] : 'default';
2. $result = $x ?: 'default';
3. $param = $_GET['param'] ?? 'default';

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實驗

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1

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通常在檢查變數用的

$param = isset($_GET['param']) ? $_GET['param'] : 'default';

檢查GET param變數。
如果有值，就用傳進來的。
如果沒有，就用 'default'

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2

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$result = $x ?: 'default';

更簡單的寫法，在php 5.3以後才能用
如果x是null，則返回default
簡單寫個測試用的就知道了

file: test2.php
<?php

$x = null;
$result = $x ?: 'default';
echo $result."\n";

$x = "abc";
$result = $x ?: 'default';
echo $result."\n";
?>

root@raspberrypi:~# /opt/php/bin/php test2.php
default
abc

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3

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$param = $_GET['param'] ?? 'default';

如果想要更潮一點，可以用php7的語法
官方的Null coalescing operator解釋

The null coalescing operator (??) has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with isset().
 It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.

節錄一下程式碼部分

<?php
// Fetches the value of $_GET['user'] and returns 'nobody'
// if it does not exist.
$username = $_GET['user'] ?? 'nobody';
// This is equivalent to:
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';

// Coalescing can be chained: this will return the first
// defined value out of $_GET['user'], $_POST['user'], and
// 'nobody'.
$username = $_GET['user'] ?? $_POST['user'] ?? 'nobody';
?>

一樣做個小實驗

file: test3.php
<?php
$username = $a ?? $b ?? 'nobody';
echo $username."\n";

$c = "weij var C";
$username2 = $c ?? $d ?? 'nobody';
echo $username2."\n";

$f = "weij var F";
$username3 = $e ?? $f ?? 'nobody';
echo $username3."\n";


$g = "weij var G";
$h = "weij var H";
$username3 = $g ?? $h ?? 'nobody';
echo $username3."\n";

?>

root@raspberrypi:~# /opt/php/bin/php test3.php
nobody
weij var C
weij var F
weij var G

從結果可以看出，如果不是null，在第一個就會返回答案
如果一路都是null，則直接返回nobody
這個糖果有點甜吶 XD