Immutability and arrays

[rumbu]

On Tuesday, 14 December 2021 at 12:13:23 UTC, Stanislav Blinov 
wrote:
>
> Because is(typeof(immutable(ComplexStruct).x) == 
> immutable(int[])). Can't bind an array of immutable to array of 
> mutable. This would require a deep copy, i.e. copy constructor.

This means that the only way to write a generic function which 
copies an array of immutable elements to another array is this:

```d
     void copy10(T)(T[] dst, immutable(T)[] src)
     {
         static if (is(immutable(T): T))
         	dst[0..10] = src[0..10];
          else
             dst[0..10] = cast(T[])src[0..10]; // or better a deep 
copy
     }
```

Btw, tried to give ComplexStruct a some copy constructors 
(casting away immutable is just for the example, I know it's not 
the way to do it).

```d
     struct ComplexStruct
     {
        int[] x;
     	
        this(ref return scope ComplexStruct another)
        {
            this.x = another.x;
        }

        this(ref return scope immutable(ComplexStruct) another)
        {
            this.x = cast(int[])(another.x);
        }
     }
```

Still slice assignment does not work. I think I will drop 
immutability, it's too complicated to work with.