I like it. Only exception is:
```
fn&() => ...;
```
Which I would prefer to see reserved for the purpose that you've written as:
```
fn() use(&) => ...;
```
The & symbol of "return by ref", should be placed on the right of the
parentheses, near the return type:
```
fn(int &$x)&: int => $x;
fn(&$x)& => $x;
```
The same thing could be allowed on regular functions and methods. currently
you'd write
```
public function &bar(): int{ /* ... */ }
public function &baz(){ /* ... */ }
```
Since 7.4 one would be allowed to write this to mean the same thing:
```
public function bar()&: int{ /* ... */ }
public function baz()&{ /* ... */ }
```
Would you guys agree on making a second RFC later changing this after and
if this RFC passes and before 7.4 is released?
