Set array or variable from constructor

//code
import std.stdio;
/**

This is a 3D Model representation.

author: *****************@gmail.com
*/
public class Model {

    private real[][][] array;

    this(ulong width, ulong height, ulong depth){
        array = new real[width][height][depth];
    }
}
// end code

//error:
************  Running DUB build  ************
> dub build
Building genesis3d ~master configuration "application", build type debug.
Compiling using dmd...
source\genesis3d\core\Model.d(13): Error: variable width cannot be read at compile time
source\genesis3d\core\Model.d(13): Error: variable width cannot be read at compile time
FAIL .dub\build\application-debug-windows-x86-dmd_2066-D0A4BE7D622326D497E72B3C1FB3A1FD\ genesis3d executable
Error executing command build:
dmd failed with exit code 1.
  ^^^ Terminated, exit code: 2 ^^^