@system blocks and safer @trusted (ST) functions

Dominikus Dittes Scherkl dominikus at scherkl.de
Mon Jul 26 09:08:05 UTC 2021

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 
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:

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

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