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If that was so, there wouldn't have been a need for the unsafe mode.

by fooker 8y ago

PudgePacket 8y ago
You're argument doesn't really make sense. Not all abstractions are workarounds for "unsafe" things. For example, unsafe is needed for dealing with the OS, no amount of abstraction will help you there. At some point you must talk to and accept memory that another process (OS) tells you is correct. I'm not so knowledgeable in Rust so I can't say definitely, but I think you should back up your statement with some (any) examples.
zacmps 8y ago
Unsafe does not exist for performance. Quoting from the rust book: > Unsafe Rust exists because, by nature, static analysis is conservative. When the compiler is trying to determine if code upholds the guarantees or not, it’s better for it to reject some programs that are valid than accept some programs that are invalid. That inevitably means there are some times when your code might be okay, but Rust thinks it’s not! In these cases, you can use unsafe code to tell the compiler, “trust me, I know what I’m doing.” The downside is that you’re on your own; if you get unsafe code wrong, problems due to memory unsafety, like null pointer dereferencing, can occur. > There’s another reason Rust has an unsafe alter ego: the underlying hardware of computers is inherently not safe. If Rust didn’t let you do unsafe operations, there would be some tasks that you simply could not do. Rust needs to allow you to do low-level systems programming like directly interacting with your operating system, or even writing your own operating system! That’s one of the goals of the language. Let’s see what you can do with unsafe Rust, and how to do it.
- steveklabnik 8y ago
  As the person who wrote those paragraphs, yes. The fundamental reason unsafe exists is not for performance reasons. That being said, the parent is also true that sometimes, unsafe is used to enhance performance. But that's not the usual case, and in fact, can even hurt performance in ways. For example, &mut T can't alias, but *mut T can, and so &mut T can be optimized more aggressively. (We recently turned these optimizations back on: https://github.com/rust-lang/rust/pull/50744 https://github.com/rust-lang/rust/pull/50744 )
EugeneOZ 8y ago
https://blog.rust-lang.org/2015/05/11/traits.html https://blog.rust-lang.org/2015/05/11/traits.html

If that was so, there wouldn't have been a need for the unsafe mode.

by fooker 8y ago

If that was so, there wouldn't have been a need for the unsafe mode.

You're argument doesn't really make sense. Not all abstractions are workarounds for "unsafe" things. For example, unsafe is needed for dealing with the OS, no amount of abstraction will help you there. At some point you must talk to and accept memory that another process (OS) tells you is correct. I'm not so knowledgeable in Rust so I can't say definitely, but I think you should back up your statement with some (any) examples.

zacmps 8y ago

Unsafe does not exist for performance. Quoting from the rust book: > Unsafe Rust exists because, by nature, static analysis is conservative. When the compiler is trying to determine if code upholds the guarantees or not, it’s better for it to reject some programs that are valid than accept some programs that are invalid. That inevitably means there are some times when your code might be okay, but Rust thinks it’s not! In these cases, you can use unsafe code to tell the compiler, “trust me, I know what I’m doing.” The downside is that you’re on your own; if you get unsafe code wrong, problems due to memory unsafety, like null pointer dereferencing, can occur. > There’s another reason Rust has an unsafe alter ego: the underlying hardware of computers is inherently not safe. If Rust didn’t let you do unsafe operations, there would be some tasks that you simply could not do. Rust needs to allow you to do low-level systems programming like directly interacting with your operating system, or even writing your own operating system! That’s one of the goals of the language. Let’s see what you can do with unsafe Rust, and how to do it.

steveklabnik 8y ago
As the person who wrote those paragraphs, yes. The fundamental reason unsafe exists is not for performance reasons. That being said, the parent is also true that sometimes, unsafe is used to enhance performance. But that's not the usual case, and in fact, can even hurt performance in ways. For example, &mut T can't alias, but *mut T can, and so &mut T can be optimized more aggressively. (We recently turned these optimizations back on: https://github.com/rust-lang/rust/pull/50744 https://github.com/rust-lang/rust/pull/50744 )

EugeneOZ 8y ago

https://blog.rust-lang.org/2015/05/11/traits.html https://blog.rust-lang.org/2015/05/11/traits.html