Copying array with const correctness

[Vindex9]

I'm trying to write a function for copying an array. But 
something strange is happening with the const correctness. I 
cannot remove the constitution for the case of a two-dimensional 
array of lines.

```d
import std.stdio;
import std.traits : Unconst;

auto copyArray(T)(const T[] arr) if (!is(T == class)) {
     alias E = Unconst!T;
     E[] copy = new E[arr.length];

     writeln("orig type: ", typeid(T));  // orig type: 
const(immutable(char)[])[]
     writeln("copy type: ", typeid(E));  // copy type: 
const(immutable(char)[])[]
     writeln("copy type: ", typeid(Unconst!E));  // copy type: 
const(immutable(char)[])[]

     static if (is(T : const(E)[])) {  // if inner array (doesn't 
work)
         writeln("No");
         for (size_t i = 0; i < arr.length; i++) {
             copy[i] = copyArray(arr[i]);
         }
     } else {
         for (size_t i = 0; i < arr.length; i++) {
             E elem = arr[i];
             copy[i] = elem;
         }
     }
     return copy;
}


void main() {
	const string[][] arr = [["ABC", "DEF"], ["GHI", "JKL"]];
     writeln(typeid(arr));  // 
const(const(const(immutable(char)[])[])[])
     auto res = copyArray(arr);
     writeln(typeid(res));  // const(immutable(char)[])[][]
}
```

What am I doing wrong?
I want a safe copy: `const string[][] -> string[][]`.