php - why are assignments in conditions bad?

Question

I am using NetBeans for PHP 6.5.

In my code I frequently use the following type of command:

if (($row = $db->get_row($sql))) {
        return $row->folder;
    } else {
        return FALSE;
    }

Netbeans tells me that I should not be using assignments in the IF statement.

Why ?

Answer 1

They are not bad, but they can lead to dangerous mistakes.

In c like languages, where an assignment is an expression, (to support for example a=b=c=1;) a common error is:

if (a = 1) { .. }

But you wanted to have

if (a == 1) { .. }

Some developers have learned to type

if (1 == a) { .. }

To create an error if one '=' is forgotten. But I think that it does not improve the readability.

However modern compilers, give a warning if you write

if (a = 1) { .. }

which I think is a better solution. In that case you are forced to check if it was what you really meant.