I can't tell if you're trolling but `unsafe { crash() }` is safe from the compiler's perspective. Otherwise you wouldn't be able to achieve anything in 'safe' rust, even print to stdout.

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flomo 3 hours ago | parent [-]

I think its a good question, just because the whole UB thing is such an ideological shibboleth.

Maybe its better to think about this in the reverse, where C and C++ has 'defined behavior', but unsafe rust intentionally does not, its just whatever the complier and platform lets you get away with. Ultimately its still just a computer which stores values in memory and jumps to subroutines.

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AlotOfReading 2 hours ago | parent [-]

Every language has defined behavior. It's what you expect to happen through a program's execution. Sometimes there will be multiple possibilities, but you can still define them regardless. Laying this out explicitly is the purpose of a standard.

Undefined behavior is everything else. C and C++ are relatively unique in that their standards explicitly say "combining these constructs in this way is undefined", and we call those cases explicit UB. There's also a larger universe of implicit UB that standards omit. Most (all?) languages have implicit UB, even if they lack the explicit stuff. What happens when you get ENOMEM is a common one.

Rust does something similar to C/C++ and lists a bunch of UB that's only possible with incorrect code in unsafe blocks. Correct code placed in an unsafe block remains defined, as does code without unsafe (up to compiler/language bugs).

	▲	flomo 31 minutes ago \| parent [-]
		Yeah, if I understand correctly, the Rust project has no intention to formally 'define' what unsafe actually does, so its very implicit. Could be anything... so it's the Does It Work? standard.