@system blocks and safer @trusted (ST) functions

[Dominikus Dittes Scherkl]

On Sunday, 25 July 2021 at 17:47:40 UTC, Paul Backus wrote:

> ```d
> @system {
>    return array.ptr[favoriteNumber()];
> }
> ```
>
> I make the following claims:
>
> 1. This code is memory-safe.

No, it's not. You use something that is not a literal, so it may 
change.
Even for a constant this should be checked for each new compile.
I would do that even if it actually were a literal, but here we 
have a function call!
The definition of the called function may be far away. How would 
this ever pass a review?
The only way to make this memory safe, is to actually test it:

```d
@system {
    assert(array.length > favoriteNumber());
    return array.ptr[favoriteNumber()];
}
```