Question

From here: https://stackoverflow.com/a/3473454/499125

int ( &fillarr( int (&arr)[5] ) )[5] { // no decay; argument must be size 5
    return arr;
}

The definition above can force the compiler to become size-aware of its parameters. This statement seems complex to me. Can someone give an anatomy of this statement or explain how does the statement achieves the size-awareness?

Can this be extended to handle multiple parameters?

Answer 1

It all boils down to being able to read the declaration. A simpler way of writing exactly the same would be:

typedef int int5[5]; // create a typedef
int5& fillarr( int5& ) {
}

As of the exact way of reading the original declaration, just break it into pieces:

int (&fillarr( int (&arr)[5] ))[ 5 ];
               ^^^^^^^^^^^^^           // A: reference to array of 5 int
^^^^^^                        ^^^^^^   // B: reference to array of 5 int
      ^^^^^^^^               ^         // C: function taking A and returning B