Why dynamic array is InputRange but static array not.

[Jonathan M Davis]

On Tuesday, September 24, 2019 1:35:24 AM MDT lili via Digitalmars-d-learn 
wrote:
> Hi:
>    in phobos/std/range/primitives.d has this code
>   ```
>     static assert( isInputRange!(int[]));
>     static assert( isInputRange!(char[]));
>     static assert(!isInputRange!(char[4]));
>     static assert( isInputRange!(inout(int)[]));
>      ```
>   but the dynamic array and static array neither not has
> popFront/front/empty.
> https://dlang.org/spec/arrays.html#array-properties properties

Because for something to be a range, it must be possible for it to shrink.
popFront works with a dynamic array, because dynamicy arrays have a dynamic
size. It's basically just

void popFront(T)(ref T[] a)
{
    a = a[1 .. $];
}

However, static arrays have a fixed size, so it's not possible to implement
popFront for them. If you want to use a static array as a range, then you
need to slice it to get a dynamic array - though when you do that, make sure
that the dynamic array is not around longer than the static array, because
it's just a slice of the static array, and if the static array goes out of
scope, then the dynamic array will then refer to invalid memory.

- Jonathan M Davis