about c++ conversion : no known conversion for argument 1 from ‘[some_class]' to ‘[some_class]&’
You are passing a temporary Base object here:
b.something(Base());
but you try to bind that to a non-const lvalue reference here:
void something(Base& b){}
This is not allowed in standard C++. You need a const reference.
void something(const Base& b){}
When you do this:
Base c;
b.something(c);
you are not passing a temporary. The non-const reference binds to c.
In the first case you attempt to pass a (non-const)reference to a temporary as argument to a function which is not possible. In the second case you pass a reference to an existing object which is perfectly valid.