Array start index

[Ali Çehreli via Digitalmars-d-learn]

On 02/07/2017 02:11 AM, Bastiaan Veelo wrote:

 >     void init() {
 >         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;
 >     }

You forgot to call that most important function. ;)

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

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;
}

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;

Ali