reference parameter should be checked.

[ghost]

struct Foo{}

fn need_ref(f &Foo){}

fn main(){
	f := Foo{}
	need_ref(f)  // should be passed reference only.
}

Currently, need_ref(f) is legal, but it can easily cause bugs.
Therefore, it would be better to prohibit it and make sure that parameters passed to need_ref() are references.

[ghost]

This system of automatic conversion of references may seem convenient, but it is actually a source of trouble.
I have heard that the intention is to discontinue automatic conversion of references, and I hope that this will be corrected as soon as possible.