PHP本身是否支持连接和析取？ [英] Does PHP support conjunction and disjunction natively?

问题描述

Javascript使用连接和析取运算符。

Javascript employs the conjunction and disjunction operators.

如果可以将其评估为：false，则返回左操作数，如果是连接（ a&& b），或者在析取的情况下为真（a || b）;否则返回右操作数。

PHP中是否存在等效运算符？

Do equivalent operators exist in PHP?

推荐答案

PHP支持短路评估，与JavaScript的结合略有不同。我们经常看到使用短路评估来测试PHP中MySQL查询结果的示例（即使不是很好的做法）：

PHP supports short-circuit evaluation, a little different from JavaScript's conjunction. We often see the example (even if it isn't good practice) of using short-circuit evaluation to test the result of a MySQL query in PHP:

// mysql_query() returns false, so the OR condition (die()) is executed.
$result = mysql_query("some faulty query") || die("Error");

请注意，当在PHP中存在要评估的表达式时，短路评估可以正常工作布尔运算符，它将产生一个返回值。只有当左侧为假时，它才会执行右侧。这与JavaScript不同：

Note that short-circuit evaluation works when in PHP when there is an expression to be evaluated on either side of the boolean operator, which would produce a return value. It then executes the right side only if the left side is false. This is different from JavaScript:

只需：

$a || $b

将返回一个布尔值 TRUE 或 FALSE 如果其中任何一个是真的或两者都是假的。它将 NOT 返回 $ b 的值，如果 $ a 是假的：

would return a boolean value TRUE or FALSE if either is truthy or both are falsy. It would NOT return the value of $b if $a was falsy:

$a = FALSE;
$b = "I'm b";

echo $a || $b;
// Prints "1", not  "I'm b"

所以要回答问题是，PHP将对这两个值进行布尔比较并返回结果。它不会返回两者的第一个真值。

So to answer the question, PHP will do a boolean comparison of the two values and return the result. It will not return the first truthy value of the two.

在PHP中更具惯用性（如果存在惯用的PHP这样的东西）将使用三元操作：

More idiomatically in PHP (if there is such a thing as idiomatic PHP) would be to use a ternary operation:

$c = $a ? $a : $b;

// PHP 5.3 and later supports
$c = $a ?: $b;
echo $a ?: $b;
// "I'm b"

PHP 7更新

PHP 7引入了 ?? null合并运算符，它可以作为更接近于连词的近似值。它特别有用，因为它不需要你在左操作数的数组键上检查 isset（）。

Update for PHP 7

PHP 7 introduces the ?? null coalescing operator which can act as a closer approximation to conjunction. It's especially helpful because it doesn't require you to check isset() on the left operand's array keys.

$a = null;
$b = 123;
$c = $a ?? $b;
// $c is 123;

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