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Trait is not a type, Any is just a custom trait. Types: https://doc.rust-lang.org/book/second-edition/ch03-02-data-types.html https://doc.rust-lang.org/book/sec
by EugeneOZ 8y ago
Trait is not a type, Any is just a custom trait. Types: https://doc.rust-lang.org/book/second-edition/ch03-02-data-types.html https://doc.rust-lang.org/book/second-edition/ch03-02-data-t...
You can create trait with name "Magic" or "Fuck" and it will not mean anything.
Pointers is not a type also.
- foldr 8y agoPointers are certainly types in Rust, and although it's of course true that the Any trait is not itself a type, a reference to an Any trait (which is what you'd actually pass around) is a type.
- EugeneOZ 8y agoWell, you can repeat it many times but it will not become true. I gave you link to the list of Rust types. Pointers are pointers, not types. Traits can have any name, their names mean nothing.
- foldr 8y agohttps://doc.rust-lang.org/book/first-edition/raw-pointers.html https://doc.rust-lang.org/book/first-edition/raw-pointers.ht... *const u32 (for example) is a clearly a Rust type -- a const pointer to an unsigned 32-bit integer, analogous to const uint32_t *p in C/C++. I'm not sure what you mean about trait names. The purpose of the Any trait is to make it possible to pass around values of any type and dynamically downcast them, as the documentation indicates. That is a safe analogue of casting a void pointer to another type.
- EugeneOZ 8y agoTo be dynamic, "Any" should be able to represent literally ANY type. As you can find, Any is a reflection-wise trait to work with static types. It's not something what you can use when you don't know type and language will dynamically convert it. You can't write fn example(foo: Any) -> u32 { foo+55 } as you CAN do in dynamic languages. Do you understand me now? Or we will keep talking about unsafe extra special types?
- rhencke 8y agoPlease remember there's a genuine human on the other end, trying to have a respectful conversation with you.
- EugeneOZ 8y agoOr there is a person who is trying to prove his offtopic point by some pedantic interruptions, which are far from the main idea of discussion.
- foldr 8y agoYou can do that if you change it to &Any and then downcast. See the docs for examples. If the issue is that you have to downcast, then your initial claim that Rust lacks void pointers was irrelevant even if true, since you also have to downcast a void pointer in C before you can perform operations on the type that it's actually pointing to.
- EugeneOZ 8y ago> If the issue is that you have to downcast It's the difference between dynamic language and language with synthetic type for reflections.
- xfer 8y agoYou can't downcast it to anything you want, it returns an Option, void pointers in C are not certainly the same, it's unsafe.
- foldr 8y agoI know. That's why I said it's "a safe analogue of casting a void pointer to another type".
- drb91 8y agoOk, type bound. You can still easily pass around data whose type is not concretely defined at the compilation step. Unless you’re arguing that the dynamic type is actually static, in which case this whole conversation seems semantically pointless.
- EugeneOZ 8y ago2 hours ago I answered it already. If you're another person who wants to convince me that Rust has same thing as Dart's "dynamic" type, then please make my code example to compile (without modifications, for literally ANY type, as in Dart) and I will say I was wrong.
- drb91 8y agoDart type or rust type? They refer to different things, which is the source of the confusion, but they're both strongly typed. In any case, you're moving the goal post from "concrete type at compile time" to "can represent any type", which is inherently going to be specific to how the language defines types. This is not an especially useful type of dynamic representation so I'm not sure why it would be desirable.
- EugeneOZ 8y agoThere is no confusion. Rust doesn't have dynamic type and Dart does. That's it. Any talks about special traits in Rust are offtopic, while code I wrote as example can't be compiled in Rust and can perfectly work in Dart. I wasn't trying to argue about words or terms, I was trying to say the gist: Dart has dynamic type, so you can send to your function any type and this function will just use it, without any downcasting - language will take care about it; and Rust doesn't have such type: you can't even compile code which is trying to work with variables like you can do in dynamic languages. But then all of that useless arguing... It's really funny when I see how people are trying to prove that Rust has same dynamic type as Dart. The very nature of these languages is different.
- leshow 8y agoA pointer is absolutely a type in rust. let i: u32 = 1; let p_imm: const u32 = &i; Look at the const u32 in the type position. The rust book even refers to const and mut pointers as types.
- EugeneOZ 8y agoconst and mut are not types, it's modifiers of mutability. On both lines type is u32z
- foldr 8y agoThe asterisks in leshow's comment are being lost in the formatting, since HN uses them for italicization. So the last line, for example, is: The rust book even refers to *const and *mut pointers as types.
- EugeneOZ 8y agoI really can't believe how stupid people can be to say "const" is a type. Even if Klabnik will say it into my face it will not be true, I don't care about the book he wrote.
- foldr 8y agoleshow said that *const u32 is a type, not that 'const' is a type. HN's formatting removed the asterisk, as it uses asterkisks for italicization.
- leshow 8y agoThe asterisk was formatted out. Read the book, they are types.
- EugeneOZ 8y agoSo you can write "let x:const = 5"? if "const" is a type.