php - !$variable = $variable inside if -

i gnawing on basics of php socket servers , client here.

then stumbled upon these lines (excerpt above links first example, happens inside while):

if (false === ($buf = socket_read($msgsock, 2048, php_normal_read))) {     echo "socket_read() failed: reason: " . socket_strerror(socket_last_error($msgsock)) . "\n";     break 2; }  if (!$buf = trim($buf)) {     continue; } 

i'm okay reading part, , closing connection in case there error reading.

but next if driving me nuts.
firstly, i'm confused how 1 may , need assign value boolean.
secondly, have trouble understanding whole expression altogether.

could please explain happens inside if, , how applies server context?

p.s. please excuse me if question isn't asked. i'm confused happens there , have no idea ask for.

with statement, there's no assignment boolean. we're comparing type of false , value of false (true false, not merely 0). can read here

if (false === ($buf = socket_read($msgsock, 2048, php_normal_read))) 

then

if (!$buf = trim($buf)) {     continue; } 

this same as

$buf = trim($buf); if ($buf == false) {   continue; } 

so, explain original:

// assignment happens first , we're checking boolean value if (!$buf = trim($buf))