Why can't I pass a const array to a function that takes scope const arrays?

[Paul Backus]

On Monday, 17 February 2020 at 20:08:24 UTC, Adnan wrote:
> On Monday, 17 February 2020 at 14:34:44 UTC, Simen Kjærås wrote:
>> On Monday, 17 February 2020 at 14:04:34 UTC, Adnan wrote:
>>> //
>>
>> All in all, I end up with this code:
>>
>> module strassens_matmul
>> package {
>>     T[][] mulIterative(T)(const T[][] mat1, const T[][] mat2) {
>>         auto result = createMatrix!T(getRowSize!T(mat1), 
>> getColumnSize!T(mat2));
>>         foreach (row; 0 .. mat1.getRowSize()) {
>>             foreach (column; 0 .. mat2.getColumnSize()) {
>>                 T value;
>>                 foreach (i; 0 .. mat1.getRowSize()) {
>>                     value += mat1.getPointCopy(row, i) * 
>> mat2.getPointCopy(i, column);
>>                 }
>>                 *result.getPointPtr(row, column) = value;
>>             }
>>         }
>>         return result;
>>     }
>> }
>
> Aren’t these passing by values? That’s why I used ref. Plus 
> since I don’t want to change the arrays in the function scope I 
> used const scope.

In D, the type `T[]` is not an array like in C, but a slice, 
containing a pointer to some data and an integer indicating the 
array's length. So when you pass it to a function by value, only 
the pointer and length are copied, not the data itself.

You can read more about D's slices in this article: 
https://dlang.org/articles/d-array-article.html