161–170 of 405 posts
>For instance, why do you have to call to_string() on a thing that’s already a string? It's so hard for me to take Rust seriously when I have to find out answers to unintuitive question like this
I’m not sure why it’s counterintuitive that &str and String are different things. Do you also find it counterintuitive in C++ that std::string is different from const char* ? What about &[u8] and Vec ?
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Rust design decisions are pretty hard to understand sometimes, Mojo is another language with a borrow-checker but it is not nearly as hard to learn as Rust due to making a few decisions. First is value semantics, in Rust people are told to always clone when learning, why isn't this semantics built into the language? It is what you have in most static languages - C, C++, Go, etc. This is the mental model many people c…
Because cloning as opposed to copying is expensive and it generates a new instance of a type. In C, you don't clone, you simply copy the struct or pointer, which will lead to a pointer to the same memory or a struct with members pointing to the same memory.
C++ on the other hand has a copy constructor, and you have to move explicitly, often generating unnecessary copies (in the sense of clone)
> Mojo's lifetime does not tell the compiler when a value is safe to use but when it is safe to delete,
What happens if you pass the variable mutably to a function?
Earlier quoted context omitted.
Rust has better defaults for types than C++, largely because the C++ defaults came from C. Rust is more ergonomic in this regard. If you designed C++ today, it would likely adopt many of these defaults. However, for high-performance systems software specifically, objects often have intrinsically ambiguous ownership and lifetimes that are only resolvable at runtime. Rust has a pretty rigid view of such things. In thes…
Interestingly, CPU-bound high-performance systems are also incompatible with Rust’s model. Ownership for them is unambiguous, but Rust has another issue, doesn’t support multiple writeable references of the same memory accessed by multiple CPU cores in parallel. A trivial example is multiplication of large square matrices. An implementation needs to leverage all available CPU cores, and a traditional way to do that y…
For your concrete example of subdividing matrixes, that seems like it should be fairly straightforward in Rust too, if you convert your mutable reference to the data into a pointer, wrap your pointer arithmetic shenanigans in an unsafe block and add a comment at the top saying more or less "this is safe because the different subprograms are always operating on disjoint subsets of the data, and therefore no mutable aliasing can occur"?
Python is my favourite, C is elegance in simplicity and Go is tolerable.
It's like reading "A Discipline of Programming", by Dijkstra. That morality play approach was needed back then, because nobody knew how to think about this stuff. Most explanations of ownership in Rust are far too wordy. See [1]. The core concepts are mostly there, but hidden under all the examples. - Each data object in Rust has exactly one owner. - Ownership can be transferred in ways that preserve the one-owner ru…
And what is that? Its easy to fall in the trap of making explanations that is very good (if you already understand).
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That's not explaining ownership, that motivating it. Which is fine. The thing that's hard to explain and learn is how to read function signatures involving (...) -> &'a [&'b str] or whatever. And how to understand and fix the compiler errors in code calling such a function.
Is it a lot different from std::unique_ptr in C++? I thought the Rust Book was too verbose but I liked Comprehensive Rust: https://google.github.io/comprehensive-rust/ I felt like I understood the stuff in the book based on cursory reading, but I haven't tried to actually use it.
Is knowing C++ a pre-requisite?
Earlier quoted context omitted.
Rust design decisions are pretty hard to understand sometimes, Mojo is another language with a borrow-checker but it is not nearly as hard to learn as Rust due to making a few decisions. First is value semantics, in Rust people are told to always clone when learning, why isn't this semantics built into the language? It is what you have in most static languages - C, C++, Go, etc. This is the mental model many people c…
> people are told to always clone when learning, why isn't this semantics built into the language? Because cloning as opposed to copying is expensive and it generates a new instance of a type. In C, you don't clone, you simply copy the struct or pointer, which will lead to a pointer to the same memory or a struct with members pointing to the same memory. C++ on the other hand has a copy constructor, and you have to m…
What happens in what manner? Mojo uses ASAP memory model, values will always be destroyed at the point of its last use. Mojo dataflow analysis will track this.
In terms of safety, Mojo will enforce `alias xor mutability` - like in Rust.
> C++ on the other hand has a copy constructor, and you have to move explicitly, often generating unnecessary copies (in the sense of clone)
Mojo also has copy and move constructors, but unlike in C++ these are not synthesised by default; the type creator has to either explicitly define the constructors or add a synthesiser. In Mojo, you can have types that are not copyable and not movable, these types can only be passed by reference. You can also have types that are copyable but not movable, or movable but not copyable.
My problem with rust is not the learning curve, but the absolute ugliness of the syntax. It's like Perl and C++ template metaprogramming had a child. I just can't stand it. Python is my favourite, C is elegance in simplicity and Go is tolerable.
Wait. What's wrong with this statement?
It's like reading "A Discipline of Programming", by Dijkstra. That morality play approach was needed back then, because nobody knew how to think about this stuff. Most explanations of ownership in Rust are far too wordy. See [1]. The core concepts are mostly there, but hidden under all the examples. - Each data object in Rust has exactly one owner. - Ownership can be transferred in ways that preserve the one-owner ru…