I am not sure, but perhaps both functions should compile:


immutable(string)[] foo() pure {
    char[][] a;
    return a; // OK
}
string[] bar() pure {
    char[][] b;
    return b; // Error
}
void main() {}


DMD 2.066alpha gives:

test.d(7,12): Error: cannot implicitly convert expression (b) of type char[][] to string[]