And having a special data-and-length type would make these guarantees... how? You're ultimately going to need to be able to create these objects from bare data and length somehow, so it's a case of garbage-in-garbage-out.
int raw_arr[4] = {0,0,0,0};
struct SmartArray arr;
arr.length = 4;
arr.val = raw_arr;
some_function(arr);
smart_int_arr arr[4] = {0,0,0,0};
some_function(arr);
Here are some other ways to declare your struct without needing as much boiler plate per declaration.
#define MAKE_SMARTARRAY(_smartarr, _array) \
do {\
_smartarr.val = (_array);\
_smartarr.len = sizeof((_array))/sizeof((_array[0]));\
}while(0)
struct SmartArray
{
int *val;
int len;
};
int main()
{
int array[] = {0,0,0,0};
struct SmartArray arr = {.val = array,
.len = sizeof(array)/sizeof(array[0])};
struct SmartArray arr2;
struct SmartArray arr3;
MAKE_SMARTARRAY(arr2, ((int[]){5,6,7,8}));
MAKE_SMARTARRAY(arr3, array);
return 0;
}