Array start index

[Bastiaan Veelo via Digitalmars-d-learn]

On Tuesday, 7 February 2017 at 20:28:30 UTC, Ali Çehreli wrote:
> You forgot to call that most important function. ;)

Hah of course. I assumed the name would give it some special 
meaning, like postblit.

> 1) I don't understand the first assert there, which does not 
> pass for me, so I commented it out.

The intention is to check that (_payload.ptr - first) is larger 
than 0.

> 2) May bad: init() is not a good name for a struct member, so 
> it should be renamed:
>
>     void initialize() {
>         // assert( first < cast(size_t)_payload.ptr);
>    // Address space underrun.
>         assert(-first < size_t.max - cast(size_t)_payload.ptr); 
> // Address space overrun.
>         this._ptr = _payload.ptr - first;
>     }
>
> 3) Instead of having to remember to call it, let's introduce a 
> function that does it for us:
>
> auto makeStaticArray(T, ptrdiff_t first, ptrdiff_t last)() {
>     auto s = StaticArray!(T, first, last)();
>     s.initialize();
>     return s;
> }

OK good.

> unittest {
>     // StaticArray!(int, -10, 10) arr;
>     auto arr = makeStaticArray!(int, -10, 10);
>
> >     foreach (i, ref e; arr)
> >         e = i;
>
> Unrelated: That line passes because you're building 32-bits. 
> Here is the error I got:
>
>   Error: cannot implicitly convert expression (i) of type long 
> to int
>
> You can cast it:
>
>         e = cast(int)i;
>
> or by
>
>         import std.conv : to;
>         e = i.to!int;

Thanks a lot for your illustrative answers, including the next 
one!

Bastiaan.