Hello i'm trying to figure out this thing..
Say i have this code.
int a = 5;
double& b = a; //Error.
Then once I've declared the second line as a const the compiler doesn't complain anymore.
const double& b = a; //Correct.
what is really going on behind the scene, why const solves the problem.
An int needs to be converted to double first. That conversion yields a prvalue temporary and these can't bind to references to non-const.
A reference to const will extend the lifetime of the temporary that would otherwise be destroyed at the end of the expression it was created in.
{
int a = 0;
float f = a; // a temporary float is created here, its value is copied to
// f and then it dies
const double& d = a; // a temporary double is created here and is bound to
// the const-ref
} // and here it dies together with d
If you're wondering what a prvalue is, here's a nice SO thread about value categories.
What's happening behind the scenes is an implicit conversion of an int to a double. The result of an implicit conversion is not an lvalue, so it cannot be used to initialize a non-const reference.
