var c:vector<char>;
// typeof(c) == ^vector<char>
c = make_vector(10, 'a'); //ok, lvalue is modifiable
c.push_back('a'); //ok

let v:vector<char>;
// typeof(v) == (const^)vector<char>
v = make_vector(10, 'b'); //not ok?
v.push_back('b'); //not ok?