sum - PHP is confused when adding and concatenating -

i have following code:

<?php      $a = 1;     $b = 2;      echo "sum: " .  $a + $b;     echo "sum: " . ($a + $b);  ?>

when execute code get:

2 sum: 3

why fail print string "sum:" in first echo? seems fine when addition enclosed in parentheses.

is weird behaviour anywhere documented?

both operators addition + operator , concatenation . operator have same operator precedence, since left associative evaluated following:

echo (("sum:" . $a) + $b); echo ("sum:" . ($a + $b));

so first line concatenation first , ends with:

"sum: 1" + 2

(now since numeric context string gets converted integer , end 0 + 2, gives result 2.)

JVParth