有人能解释Php中奇怪的行为吗？ [关闭]

Question

This is not possible in Python:

Python 2.7.3
[GCC 4.7.2] on linux2
>>> b = 15
>>> a = 15 + b = 16
  File "<stdin>", line 1
SyntaxError: can't assign to operator
>>>

I can test the same in C, C++, Java and JavaScript...

var b=15 ; var a = 15+ b = 15
VM155:2 Uncaught ReferenceError: Invalid left-hand side in assignment(…)

But can someone explain me why this works in Php, and why?

php -r '$b = 15; $a = "45". $b = 15;'

Answer 1

When an assignment happens, PHP returns the value that was assigned.

So if you were to do echo $a = 3; you would get 3 in the PHP out.

Another example from the same docs linked above:

$a = ($b = 4) + 5; // $a is equal to 9 now, and $b has been set to 4.

Simply put, it's desired behaviour in the context of the language and its documentation. Python doesn't adopt this behaviour.

Interestingly, I can also do this with other quite powerful programming languages. Here's Ruby:

vagrant@ubuntu-14:/vagrant$ irb
2.1.2 :001 > a = (b = 4) + 5
 => 9 
2.1.2 :002 > b
 => 4