What is the difference between .= and += in PHP?

What are the differences between .= and += in PHP?

Answer

Quite simply, "+=" is a numeric operator and ".=" is a string operator. Consider this example:

$a = 'this is a ';
$a += 'test';

This is like writing:

$a = 'this' + 'test';

The "+" or "+=" operator first converts the values to integers (and all strings evaluate to zero when cast to ints) and then adds them, so you get 0.

If you do this:

$a = 10;
$a .= 5;

This is the same as writing:

$a = 10 . 5;

Since the "." operator is a string operator, it first converts the values to strings; and since "." means "concatenate," the result is the string "105".