Hi,

I get the following compile error with this function below:
source\mod_data\matrices.d(66,12): Error: cannot implicitly convert expression (j) of type ulong to uint

(66,12) is [j] in row[j]

Using uint as type for rows, cols (i.e. the indices) works. Is ulong not allowed for array indices? I could not find the respective information.

Thanks!


49	private double[][] matrix_uniform(ulong rows, ulong cols, double lbound, double ubound, ulong precision)
50	{
51	  double[][] array;
52	  double[] rowT;
53	  auto gen = Random(unpredictableSeed);
54	  auto rndUniform = uniform(lbound, ubound, gen);
55	
56	  foreach(ulong i; 0..cols)
57	  {
58	    rowT ~= 0;
59	  }
60	
61	  foreach(ulong i; 0..rows)
62	  {
63	    foreach(ulong j; 0..cols)
64	    {
65	      rndUniform = uniform(lbound, ubound, gen);
66	      rowT[j] = to!double(rndUniform) / 10^^precision;
67	    }
68	    array ~= rowT.dup;
69	  }
70	    return array;
71	}

On Wednesday, October 04, 2017 09:04:10 thorstein via Digitalmars-d-learn wrote:
> Hi,
>
> I get the following compile error with this function below:
> source\mod_data\matrices.d(66,12): Error: cannot implicitly
> convert expression (j) of type ulong to uint
>
> (66,12) is [j] in row[j]
>
> Using uint as type for rows, cols (i.e. the indices) works. Is ulong not allowed for array indices? I could not find the respective information.

Array indices - and array length - are size_t. If you're on a 32-bit system, that's an alias to uint, whereas on a 64-bit system, it's an alias to ulong. In general, code should be using size_t when dealing with arrays not uint or ulong (unless you're talking about having elements of uint or ulong). If you don't use size_t, then you're likely to run into problems when compiling for a different architecture.

But if you have a ulong that you need to convert to a uint, then you can always cast or use std.conv.to!uint so long as the number will actually fit in a uint.

- Jonathan M Davis