problems with const pointers to const objects

[Tim Partridge]

Why would this be illegal?

#include <list>
using namespace std;

int main ( char argc, char* argv[] ) {
list< const int * const > l;
return 0;
}

Doesn't it make sense to be able to have a list of constant pointers that
point to constant objects, or am I missing something?

Clueless,
Tim Partridge

 

[Victor Bazarov]

Why would this be illegal?

#include <list>
using namespace std;

int main ( char argc, char* argv[] ) {
list< const int * const > l;
return 0;
}

Doesn't it make sense to be able to have a list of constant pointers that
point to constant objects, or am I missing something?

Standard containers require contained things to be Assignable (and
Copy-Constructible). While constant things are copy-constructible,
they are not assignable.

Victor

 

[Jonathan Turkanis]

Why would this be illegal?

#include <list>
using namespace std;

int main ( char argc, char* argv[] ) {
list< const int * const > l;
return 0;
}

Doesn't it make sense to be able to have a list of constant pointers that
point to constant objects, or am I missing something?

Standard containers require contained things to be Assignable (and
Copy-Constructible). While constant things are copy-constructible,
they are not assignable.

Incidentally, one of the standard workarounds for storing
non-copyconstructable or non-assignable types in standard containers
is to store pointers to instances of those types.

In this case, that means using list< const int * const* >. ;-)

Jonathan