Mastering PHP 7

Uniform variable syntax

The new variable syntax is probably one of the most impacting features of the PHP 7 release. It brings greater order into variable dereferencing. The impacting part, however, not only affects changes for better as it also introduces certain backwards compatibility (BC) breaks. Among the main reasons for these changes were inconsistencies with variable variable syntax.

Observing the $foo['bar']->baz expression, first a variable named $foo is fetched, then the bar offset is taken from the result, and, finally, the baz property is accessed. This is how normally variable accesses is interpreted, from left to right. However, the variable variable syntax goes against this principle. Observing the $$foo['baz'] variable,  ...