Using short circuiting to get first non-null variable

问题

What's the equivalent of the following (based in JS style) in PHP:

echo $post['story'] || $post['message'] || $post['name'];

So if story exists then post that; or if message exist post that, etc...

回答1:

It would be (PHP 5.3+):

echo $post['story'] ?: $post['message'] ?: $post['name'];

And for PHP 7:

echo $post['story'] ?? $post['message'] ?? $post['name'];

回答2:

There is a one-liner for that, but it's not exactly shorter:

echo current(array_filter(array($post['story'], $post['message'], $post['name'])));

array_filter would return you all non-null entries from the list of alternatives. And current just gets the first entry from the filtered list.

回答3:

Since both or and || do not return one of their operands that's not possible.

You could write a simple function for it though:

function firstset() {
    $args = func_get_args();
    foreach($args as $arg) {
        if($arg) return $arg;
    }
    return $args[-1];
}

回答4:

Building on Adam's answer, you could use the error control operator to help suppress the errors generated when the variables aren't set.

echo @$post['story'] ?: @$post['message'] ?: @$post['name'];

http://php.net/manual/en/language.operators.errorcontrol.php

回答5:

As of PHP 7, you can use the null coalescing operator:

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.

// 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';

回答6:

You can try it

<?php
    echo array_shift(array_values(array_filter($post)));
?>

回答7:

That syntax would echo 1 if any of these are set and not false, and 0 if not.

Here's a one line way of doing this which works and which can be extended for any number of options:

    echo isset($post['story']) ? $post['story'] : isset($post['message']) ? $post['message'] : $post['name'];

... pretty ugly though. Edit: Mario's is better than mine since it respects your chosen arbitrary order like this does, but unlike this, it doesn't keep getting uglier with each new option you add.

回答8:

Because variety is the spice of life:

echo key(array_intersect(array_flip($post), array('story', 'message', 'name')));

来源：https://stackoverflow.com/questions/8203755/using-short-circuiting-to-get-first-non-null-variable

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php

short-circuiting