Deep analysis of PHP operator precedence

Zhou 51 friend a piece of code to ask me, said he could not understand this code, think that this code has a problem, the code is similar:

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$array 1 = Array (1, 2); $array 2 = Array (3, 4); $result = Empty ($array 1) = = 3? $array 1: $array 2;

I think it should be the problem of operator precedence.
Logically, the problem with the precedence of these operators is that they should not appear in the project code, only to allow it in the interview question, the programmer should use parentheses in the writing code to avoid this uncertainty problem. The code in the project should be the kind of thing we know when we see the results, not what we need to do to get the results. The results of this priority code are sometimes not what we believe, and look at the following example:

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<?php if ($a = && $b = 200) { Var_dump ($a, $b); }

The above code you might think is:

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<?php if ($a = (&& $b) = 200) { Var_dump ($a, $b); }

But this is not the case, the actual result is:

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<?php if ($a = (&& $b = 200)) { Var_dump ($a, $b); }

And why is that? That's because PHP doesn't fully follow the priority definition, as explained in the PHP manual

Note:although = has a lower precedence than most other operators, PHP would still allow the expressions to the similar Ng:if (! $a = foo ()), in which case the return value of Foo () was put into $a.

Code:

Code 1:

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<?php $x =true; $y =false; $z = $y or $x;?> Code 2: <?php $x =true; $y =false; $z = $y | | $x; ?>

This code should not appear in the actual project, and should be replaced with the following code:

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$z = ($y OR $x ); $z = ($y | | $x);