Counting an initialised array, and segments

[Jonathan M Davis]

On Monday, June 26, 2023 5:08:06 AM MDT Cecil Ward via Digitalmars-d-learn 
wrote:
> On Monday, 26 June 2023 at 08:26:31 UTC, Jonathan M Davis wrote:
> > On Sunday, June 25, 2023 4:08:19 PM MDT Cecil Ward via
> >
> > Digitalmars-d-learn wrote:
> >> I recently had some problems
> >>
> >> dchar[] arr = [ ‘ ‘, TAB, CR, LF … ];
> >>
> >> and I got errors from the compiler which led to me having to
> >> count the elements in the initialiser and declare the array
> >> with
> >> an explicit size. I don’t want the array to be mutable so I
> >> later
> >> added immutable to it, but that didn’t help matters. At one
> >> point, because the array was quite long, I got the arr[
> >> n_elements ] number wrong, it was too small and the remainder
> >> of
> >> the array was full of 0xffs (or something), which was good,
> >> helped me spot the bug.
> >>
> >> Is there any way to get the compiler to count the number of
> >> elements in the initialiser and set the array to that size ?
> >> And it’s immutable.
> >
> > Without seeing the errors, I can't really say what the problem
> > was, but most character literals are going to be char, not
> > dchar, so you may have had issues related to the type that the
> > compiler was inferring for the array literal. I don't recall at
> > the moment how exactly the compiler decides the type of an
> > array literal when it's given values of differing types for the
> > elements.
> >
> > Either way, if you want a static array, and you don't want to
> > have to count the number of elements, then
> > https://dlang.org/phobos/std_array.html#staticArray should take
> > care of that problem.
> >
> > - Jonathan M Davis
>
> Where I used symbolic names, such as TAB, that was defined as an
> int (or uint)
> enum TAB = 9;
> or
> enum uint TAB = 9;
> I forget which. So I had at least one item that was typed
> something wider than a char.
>
> I tried the usual sizeof( arr )/ sizeof dchar, compiler wouldn’t
> have that for some reason, and yes I know it should be D syntax,
> god how I long for C sizeof()!

sizeof is a property in D. So, you can do char.sizeof or varName.sizeof. But
regardless, there really is no reason to use sizeof with D arrays under
normal circumstances. And in the case of dynamic arrays, sizeof will give
you the size of the dynamic array itself, not the slice of memory that it
refers to. You're essentially using sizeof on

struct DynamicArray(T)
{
    size_t length;
    T* ptr;
}

which is not going to tell you anything about the memory it points to. The
length property of an array already tells you the length of the array (be it
static or dynamic), so using sizeof like you're talking about really does
not apply to D.

And I wouldn't advise using uint for a character in D. That's what char,
wchar, and dchar are for. Depending on the circumstances, you get implicit
conversions between character and integer types, but they are distinct
types, and mixing and matching them willy-nilly could result in compilation
errors depending on what your code is doing.

- Jonathan M Davis