Question

I have been reading the PHP manual about references and something is confusing me. It says that references are not pointers to memory addresses but rather…

Instead, they are symbol table
aliases.

Isn’t this essentially a pointer if the reference points to the symbol table entry which then points to a memory address?

Edit:

Some great answers. Just want to pop this in here… How would I unset the variable for which another is pointing to?

$var = "text";
$ref =& $var;
unset($ref);

It looks like for this to work, I need to unset $var as well so the GC removes it.

Answer 1

There is a wonderful PHP References Tutorial which should explain everything in a more in depth manner than the PHP docs themselves (gasp), even going so far as to explain what happens upon variable creation.

PHP internally implements variable
values through a structure know as a
_zval_struct, generally referred to simply as a zval. In addition to
storing the value and information
about its type, the zval also
specifies a refcount. The refcount
counts the number of references to the
value and is essential to the
operation of the garbage collector,
allowing memory to be freed when it is
no longer in use.

A reference in PHP is simply a
variable corresponding to the same
zval as another variable. References
can be explicitly created using a
special form of the assignment operate
with an ampersand after the equals
sign.