[OT] Move semantics in a nutshell

[Timon Gehr]

On 11/10/25 17:13, monkyyy wrote:
> On Monday, 10 November 2025 at 12:42:10 UTC, Timon Gehr wrote:
>> In your example you also had to think about "hmmm what are the 
>> possible `T[]`. Actually you had to think about "hmmm what are the 
>> possible combinations of `int`s and `T[]`s.
> 
> That ubyte code was a static array
> ...

Sorry for not being clear, you are correct that "your example code" more 
naturally refers to the `ubyte` example due to recency bias. I was here 
talking about your earlier example with a `T[]`, where the point is even 
a bit more obvious.

> A static 256 length array with a ubyte index has no "specific 
> limitations on its bit pattern" if it fails its a os level failure and I 
> couldn't operate anyway.
> ...

The simple fact is that you are able to relate types to execution 
behavior. This is because the compiler produces binaries that are 
related in a specific way to your source code. I.e., it establishes (or 
at least aims to establish) very specific invariants on source code and 
corresponding binaries. Undefined behavior is an example of weak 
invariants, for a language without undefined behavior, these invariants 
are stronger. Your workarounds against default behaviors that result in 
crashes and/or UB are workarounds against weak invariants.

>> Look no further than encryption-based ransomware (e.g. EternalBlue 
>> exploited by WannaCry and NotPetya/ExPetr). It's not a theoretical 
>> scenario at all,
> 
> Such encryption is **very** well defined, as is what version of rm -* 
> will delete your harddrive.
> ...

The compiler produced an executable that allows an attacker to encrypt 
or wipe the hard drive remotely when none of these capabilities were 
spelled out in the source code of the program. It's a prime example of 
undefined behavior in action that illustrates that the scenarios I 
brought up are realistic in the context in which you had placed them.