c++ - Non const lvalue references

Question

Why can you do this

int a;
const double &m = a;

But when you do this

int a;
double &m = a;

you get an error?

error: non-const lvalue reference to type 'double' cannot bind to a value of unrelated type 'int'

Edit:

To be more specific I am trying to understand the reason non-const references can't bind temp objects.

Answer 1

That is because a temporary can not bind to a non-const reference.

double &m = a;

a is of type int and is being converted to double. So a temporary is created. Same is the case for user-defined types as well.

Foo &obj = Foo(); // You will see the same error message.

But in Visual Studio, it works fine because of a compiler extension enabled by default. But GCC will complain.