php - Why is it assigning value to $b? It should not as per operator precedence rule -

i trying answer why code infinite loop?

there thought issue because of operations precedence, when checked http://php.net/manual/en/language.operators.precedence.php , . has more precedence =

so tried following code :

 $a.$b = "test";   echo $a;  echo $b; 

and got undefined variable a , test means assigning value $b, how assigning value $b (should not per operations precedence)

i believe answer stated in docs:

although = has lower precedence other operators, php still allow expressions similar following: if (!$a = foo()), in case return value of foo() put $a.

expanding on jon's answer, since can't assign expression, = takes precedence , interpreter sees following statement:

$a.($b = "test"); 

so become 2 separate expressions, each following own precedence. , therefore test assigned $b.

to prove this, add assignment:

$a = 'my '; $c = $a.$b = "test";  var_dump($a); // string(3) "my " var_dump($b); // string(4) "test" var_dump($c); // string(7) "my test"