blocks|key|1311307|text|在php+5.3中有一个新的运算符可以做到这一点：?:。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1311308|//+A
echo+'A'+?:+'B';

//+B
echo+''+?:+'B';

//+B
echo+false+?:+'B';

//+B
echo+null+?:+'B';|code-block|syntax|javascript|1311309|来源：http://www.php.net/ChangeLog-5.php#5.3.0|1311310|entityMap|0|LINK|mutability|MUTABLE|url|http://www.php.net/ChangeLog-5.php#5.3.0^0|P|2|0|0|3|14|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

There is a new operator in php 5.3 which does this: <code>?:</code> 

<pre><code>// A
echo 'A' ?: 'B';

// B
echo '' ?: 'B';

// B
echo false ?: 'B';

// B
echo null ?: 'B';
</code></pre>

Source: <a href="http://www.php.net/ChangeLog-5.php#5.3.0" rel="noreferrer">http://www.php.net/ChangeLog-5.php#5.3.0</a>

blocks|key|1311514|text|PHP7引入了一个真正的coalesce+operator|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1311515|echo+$_GET['doesNotExist']+??+'fallback';+//+prints+'fallback'|code-block|syntax|javascript|1311516|如果??之前的值不存在或为null，则获取??之后的值。|style|CODE|1311517|对前面提到的?:运算符的改进是，??还可以处理未定义的变量，而不会抛出E_NOTICE。|1311518|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op^0|C|H|0|0|0|2|2|D|4|L|2|0|6|2|G|2|Z|8|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@$A|12|B|13|K|L]|$A|14|B|15|K|L]|$A|16|B|17|K|L]]|9|@]|C|$]]|$1|M|3|N|5|6|7|18|8|@$A|19|B|1A|K|L]|$A|1B|B|1C|K|L]|$A|1D|B|1E|K|L]]|9|@]|C|$]]|$1|O|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

PHP 7 introduced a real <a href="http://php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op" rel="noreferrer">coalesce operator</a>:

<pre><code>echo $_GET['doesNotExist'] ?? 'fallback'; // prints 'fallback'
</code></pre>

If the value before the <code>??</code> does not exists or is <code>null</code> the value after the <code>??</code> is taken. 

The improvement over the mentioned <code>?:</code> operator is, that the <code>??</code> also handles undefined variables without throwing an <code>E_NOTICE</code>.

blocks|key|1526214|text|在谷歌上第一次点击"php+coalesce“。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1526215|function+coalesce()+{
++$args+=+func_get_args();
++foreach+($args+as+$arg)+{
++++if+(!empty($arg))+{
++++++return+$arg;
++++}
++}
++return+NULL;
}|code-block|syntax|javascript|1526216|http://drupial.com/content/php-coalesce|offset|length|1526217|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|13|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@$I|U|J|V|1|W]]|A|$]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|H]]]]

First hit for "php coalesce" on google.

<pre><code>function coalesce() {
 $args = func_get_args();
 foreach ($args as $arg) {
 if (!empty($arg)) {
 return $arg;
 }
 }
 return NULL;
}
</code></pre>

<a href="http://drupial.com/content/php-coalesce" rel="noreferrer">http://drupial.com/content/php-coalesce</a>

blocks|key|1311402|text|我真的很喜欢?：操作符。不幸的是，它还没有在我的生产环境中实现。所以我使用的等价物是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1311403|function+coalesce()+{
++return+array_shift(array_filter(func_get_args()));
}|code-block|syntax|javascript|1311404|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I really like the ?: operator. Unfortunately, it is not yet implemented on my production environment. So I use the equivalent of this:

<pre><code>function coalesce() {
 return array_shift(array_filter(func_get_args()));
}
</code></pre>

blocks|key|1526504|text|值得注意的是，由于PHP对未初始化的变量和数组索引的处理，任何类型的合并函数的使用都是有限的。我希望能够做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1526505|$id+=+coalesce($_GET['id'],+$_SESSION['id'],+null);|code-block|syntax|javascript|1526506|但在大多数情况下，这会导致PHP在E_NOTICE中出错。在使用变量之前测试其是否存在的唯一安全方法是直接在empty()或isset()中使用它。如果您知道coalesce中的所有选项都已初始化，则Kevin建议的三元运算符是最佳选择。|1526507|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

It is worth noting that due to PHP's treatment of uninitalised variables and array indices, any kind of coalesce function is of limited use. I would love to be able to do this:

<pre><code>$id = coalesce($_GET['id'], $_SESSION['id'], null);
</code></pre>

But this will, in most cases, cause PHP to error with an E_NOTICE. The only safe way to test the existence of a variable before using it is to use it directly in empty() or isset(). The ternary operator suggested by Kevin is the best option if you know that all the options in your coalesce are known to be initialised.

blocks|key|1526354|text|确保您准确地确定了您希望此函数如何处理某些类型。PHP有各种各样的类型检查或类似的函数，所以一定要知道它们是如何工作的。这是is_null()和empty()的比较示例|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1526355|$testData+=+array(
++'FALSE'+++=>+FALSE
++,'0'++++++=>+0
++,'"0"'++++=>+"0"++
++,'NULL'+++=>+NULL
++,'array()'=>+array()
++,'new+stdClass()'+=>+new+stdClass()
++,'$undef'+=>+$undef
);

foreach+(+$testData+as+$key+=>+$var+)
{
++echo+"$key+"+.+((+empty(+$var+)+)+?+'is'+:+'is+not')+.+"+empty ";
++echo+"$key+"+.+((+is_null(+$var+)+)+?+'is'+:+'is+not')++.+"+null ";
++echo+'<hr>';
}|code-block|syntax|javascript|1526356|如您所见，empty()对所有这些函数都返回true，但is_null()只对其中两个函数返回true。|1526357|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Make sure you identify exactly how you want this function to work with certain types. PHP has a wide variety of type-checking or similar functions, so make sure you know how they work. This is an example comparison of is_null() and empty()

<pre><code>$testData = array(
 'FALSE' =&gt; FALSE
 ,'0' =&gt; 0
 ,'"0"' =&gt; "0" 
 ,'NULL' =&gt; NULL
 ,'array()'=&gt; array()
 ,'new stdClass()' =&gt; new stdClass()
 ,'$undef' =&gt; $undef
);

foreach ( $testData as $key =&gt; $var )
{
 echo "$key " . (( empty( $var ) ) ? 'is' : 'is not') . " empty&lt;br&gt;";
 echo "$key " . (( is_null( $var ) ) ? 'is' : 'is not') . " null&lt;br&gt;";
 echo '&lt;hr&gt;';
}
</code></pre>

As you can see, empty() returns true for all of these, but is_null() only does so for 2 of them.

blocks|key|1526304|text|我目前正在使用它，但我想知道它是否不能通过PHP5中的一些新功能来改进。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1526305|function+coalesce()+{
++$args+=+func_get_args();
++foreach+($args+as+$arg)+{
++++if+(!empty($arg))+{
++++return+$arg;
++++}
++}
++return+$args[0];
}|code-block|syntax|javascript|1526306|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I'm currently using this, but I wonder if it couldn't be improved with some of the new features in PHP 5.

<pre><code>function coalesce() {
 $args = func_get_args();
 foreach ($args as $arg) {
 if (!empty($arg)) {
 return $arg;
 }
 }
 return $args[0];
}
</code></pre>

blocks|key|1526553|text|PHP+5.3%2B，带有闭包：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1526554|function+coalesce()
{
++++return+array_shift(array_filter(func_get_args(),+function+($value)+{
++++++++return+!is_null($value);
++++}));
}|code-block|syntax|javascript|1526555|演示：https://eval.in/187365|offset|length|1526556|entityMap|0|LINK|mutability|MUTABLE|url|https://eval.in/187365^0|0|0|3|M|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

PHP 5.3+, with closures:

<pre><code>function coalesce()
{
 return array_shift(array_filter(func_get_args(), function ($value) {
 return !is_null($value);
 }));
}
</code></pre>

Demo: <a href="https://eval.in/187365" rel="nofollow">https://eval.in/187365</a>

Many programming languages have a coalesce function (returns the first non-NULL value, <a href="http://www.postgresql.org/docs/9.3/static/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL" rel="noreferrer">example</a>). PHP, sadly in 2009, does not.

What would be a good way to implement one in PHP until PHP itself gets a coalesce function?

Coalesce function for PHP?

许多编程语言都有一个coalesce函数(返回第一个非空值)。不幸的是，在2009年，PHP没有。在PHP本身获得coalesce函数之前，有什么好方法可以用PHP实现一个呢？

问PHP的合并函数？
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回答 8

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