PHP usage tips

1.  Instance usage 

Array overwritten after a loop
Error code:
$att = new Attachment();
for ($i=2; $i<=$parts;$i++){
$att->attachmentHeader = imap_bodystruct($imap, $msgno, $i);
$att->attachmentContent = imap_fetchbody($imap, $msgno, $i);
$attachments[$i-2] = $att; 
}
return $attachments;

All the objects in the $attachments actually refer to one instance, and this instance object is overwritten by the last $att value. That is because the instance is defined outside the for loop, and every time when the $att is updated, and the $att is updated. 

Correct code:
for ($i=2; $i<=$parts;$i++){
$att = new Attachment();
$att->attachmentHeader = imap_bodystruct($imap, $msgno, $i);
$att->attachmentContent = imap_fetchbody($imap, $msgno, $i);
$attachments[$i-2] = $att; 
}
return $attachments;

2. Be careful of "space"

When you define a string and set the value of the string, it is most possible that you will typo a "space" there, this bug can always be ignored if you do not have experience to make such a typo before, it takes me 2 hours to figure out this typo.