Concept proposal: Safely catching error

[ag0aep6g via Digitalmars-d]

On 06/07/2017 09:45 PM, ag0aep6g wrote:
> When no @trusted code is involved, then catching an out-of-bounds error 
> from a @safe function is safe. No additional rules are needed. Assuming 
> no compiler bugs, a @safe function simply cannot corrupt memory without 
> calling @trusted code.

Thinking a bit more about this, I'm not sure if it's entirely correct. 
Can a @safe language feature throw an Error *after* corrupting memory? 
For example, could `a[i] = n;` write the value first and do the bounds 
check afterwards? There's probably a better example, if this kind of 
"shoot first, ask questions later" style ever makes sense.

If bounds checking could be implemented like that, you wouldn't be able 
to ever catch the resulting error safely. Wouldn't matter if it comes 
from @safe or @trusted code. Purity wouldn't matter either, because an 
arbitrary write like that doesn't care about purity.