array/Array: "hard" bounds checking

[TheFlyingFiddle]

On Thursday, 22 February 2018 at 00:34:59 UTC, kdevel wrote:
> Is there a D equivalent of the C++ at method? I would like to 
> reformulate
>
> repro2.d
> ---
> void main ()
> {
>    import std.stdio;
>    import std.container;
>    import std.range;
>    auto z = Array!char();
>    z.reserve(0xC000_0000);
>    z.capacity.writeln;
>    z.length.writeln;
>    for (uint u = 0; u < 0xC000_0000; ++u)
>       z.insert = 'Y';
>    int i = -1073741825;
>    i.writeln;
>    z[i] = 'Q';
>    z[i].writeln;
> }
> ---
>
> $ dmd -O -m32 repro2.d
> $ ./repro2
> 3221225472
> 0
> -1073741825
> Q
>
> such that it fails like the 64 bit version:
>
> $ dmd -O -m64 repro2.d
> $ ./repro2
>
> 3221225472
> 0
> -1073741825
> core.exception.RangeError at .../dmd2/linux/bin64/../../src/phobos/std/container/array.d(650): Range violation
> ----------------
> ??:? _d_arrayboundsp [0x440d22]
> .../dmd2/linux/bin64/../../src/phobos/std/container/array.d:650 
> inout pure nothrow ref @nogc @safe inout(char) 
> std.container.array.Array!(char).Array.opIndex(ulong) [0x43bb0f]
> repro2.d:14 _Dmain [0x43afff]

Well in a 32bit program the value 0xBFFF_FFFF(-1073741825) is 
clearly inside the array. The Array class uses an size_t 
internaly for storing the length/capacity, that is uint in a 
32bit program and ulong in a 64bit program. In the 64bit the 
value (0xFFFF_FFFF_BFFF_FFFF)(-1073741825) is larger than 
0xC000_000 so it will be out of bounds in this case.

If you want any negative integer to be out of bounds the capacity 
cannot be larger than 0x7FFF_FFFF in 32bit programs.

But this behavior is strange. Well the really strange/bad part is 
that it's allowed by the compiler in the first place. I would be 
very happy if a user was forced to make an explicit cast for int 
<-> uint conversions. Like we have to do for long -> int 
conversions. Also signed/unsigned comparisons should be strictly 
outlawed by the compiler.

Eg:

uint a = 3;
int b = -1;

assert(a > b); //No idea what should happen here.