References
References at the PHP source level map fairly straightforwardly onto the internals. Consider this PHP code:
<?php $a = "Hello World"; $b =& $a; ?>
Here $b
is a reference to the
same zval
container as $a
. Internally in PHP, the is_ref
indicator is set to 1 for both the
zval
containers, and the reference
count is set to 2. If the user then does an unset($b)
, the is_ref
indicator on the $a
container is set to 0. The reference count
actually remains at 2, since the $a
symbol table entry is still referring to this zval
container and the zval
container itself also counts as a
reference when the container is not a reference itself (indicated by the
is_ref
flag being on). This may be a
little bit confusing, but keep reading.
When you allocate a new zval
container using MAKE_STD_ZVAL( )
, or
if you call INIT_PZVAL( )
directly on
a new container, the reference count is initialized to 1 and is_ref
is set to 0. If a symbol table entry is
then created for this container, the reference count becomes 2. If a
second symbol table alias is created for this same container, the
is_ref
indicator is turned on. If a
third symbol table alias is created for the container, the reference
count on the container jumps to 3.
A zval
container can have a
reference count greater than 1 without is_ref
being turned on. This is for
performance reasons. Say you want to write a function that creates an
n-element array and initializes each element to a
given value that you provide, much like PHP’s array_fill( ...
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