Fixed size multidimensional array at runtime

[Vidar Wahlberg]

I know multidimensional arrays has been brought up many times, 
although I was not able to find a clear answer to my question. My 
knowledge of what's going on behind the curtains is somewhat 
lacking, please correct me if my assumptions are incorrect.

Creating a dynamic multidimensional array can be easily achieved 
with for example "auto matrix = new int[][](4, 2);", although if 
I've understood it correct this would create a "jagged" array (as 
explained on page 112 in TDPL) which may cause efficiency issues 
due to two indirections as opposed to only one indirection which 
you would have in a "rectangular" array (as explained at 
http://dlang.org/arrays.html). If you at compile time know the 
dimensions of the array you could write "int[2][4] matrix;", and 
I've understood this as creating a "rectangular" array.

In my case I don't know the dimensions at compile time, but I'm 
still interested in creating a multidimensional array with only 
one indirection (i.e. allocated contiguously in memory) at 
runtime, where I'm not going to modify the size of the array. Is 
this impossible* in D?
*I know I could create a one-dimensional array and 
programmatically convert from multiple dimensions to one 
dimension, yet this is not as satisfactory as a "true" 
multidimensional array.

Obviously it's the efficiency I worry about, I would much 
appreciate if someone could shed light upon this.