C++ reference collapsing cheat sheet

T const T T & const T & T && const T &&
X const X X & const X & X && const X &&
X & X & X & X & X & X &
X && X && X & X & X && X &&
const X const X const X & const X & const X && const X &&
const X & const X & const X & const X & const X & const X &
const X && const X && const X & const X & const X && const X &&

Proof: https://gcc.godbolt.org/z/5HRbX3.