问题描述
> ="和"=="是非关联运算符，当它们彼此相邻时，它们将按优先级进行求值:
">=" and "==" are non-associative operators and when they are next to each other, they get evaluated by precedence:
2 >= 3 == 3
就像:
(2 >= 3) == 3 // ">=" have higher precedence over "=="
但是，如果混合中有关联运算符，甚至是较低优先级的运算符，也会根据关联运算符进行评估:
but if there is an associative operator in the mix, even lower precedence operator, it get evaluated acording to the associative operator:
var_dump($a = 2 >= $b = 3 == 3); // bool(true)
var_dump(2 >= 3 == 3); // bool(false)
这很不正常:
var_dump($a = 2 >= ($b = 3 == 3));
var_dump((2 >= 3) == 3);
我理解正确吗?
推荐答案
PHP始终仅解析定义的方式.并且必须赋予变量赋值更高(隐式)的优先级，因为赋值左侧的必须是变量.不能解析为($a = 2 >= $b) = 3 == 3.它不依赖于关联性.
PHP parses always only the defined ways. And giving variable assignments a higher (implicit) precedence is necessary as on the left of an assignment must be a variable. It's impossible to parse as ($a = 2 >= $b) = 3 == 3. It doesn't depend on the associativity.
看这个例子； &运算符是关联的(而=>不是).
Look at this example; the & operator is associative (and the => isn't).
$b = 2;
$a = 2 >= $b & 2;
在这种情况下，它是从左到右.喜欢:
In this case it is left to right. Like:
var_dump($a = ((2 >= $b) & 2)); // int (0)
var_dump($a = 2 >= $b & 2); // int (0)
比较:
var_dump($a = (2 >= ($b & 2))); // bool (true)
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