const reference in POD

[mathieu]

While trying to build a compiled time dictionary I discovered the following code. It seems to compile without a single warning on gcc. Could someone please tell me if this is legal, and why ?

$ cat demo.cxx
enum TheType {
INT = 0,
FLOAT
};

struct entry {
TheType type;
const int & val;
};

static const int I0 = 0;
static const float F0 = 0.1f;

static const entry array[] = {
{ INT, I0 },
{ FLOAT, F0 } // {float&} <=> {int&} ?
};

int main(int , char *[])
{
return 0;
}

$ g++ -Wall -pedantic demo.cxx && ./a.out

Thanks

[Ian Collins]

mathieu wrote:

*Please wrap your lines!*

I was surprised this didn't produce a warning. Another compiler (Sun
CC) says:

Warning: A class with a reference member lacks a user-defined
constructor, which can lead to errors.

Sound advice!
--
Ian Collins

[Francis Glassborow]

Yes, but nonetheless it must then compile the code because the member is
a const & and those can exist even when the initialising type is wrong
as long as a conversion exists. The code is essentially no different to:

int main(){
float const f= 2.0;
int const & i_ref = f;
// the implementation creates a temporary instance of int with the value
2 which it binds to i_ref. The temporary's lifetime will be that of
i_ref. Note that this only applies for const references. and not for
unqualified references

Francis