PHP RFC ASSIGN CALL OPERATOR

[RFC]
Title: Short syntax for assign call operator.

Intro: What is assign call operator? What does it do?
It shortens, `$x = function($x)` to `$x ASSIGN_CALL_OPERATOR function`.

Possible syntax: (=) , &= , <-(), =()

function is anything that is callable.

Please give inputs on good name and good syntax, or any other constructive feedback.