That you guys aren’t finding the value tells me you’re using the tool wrong and likely have already decided with prejudice, because I have primary experience that once you try to figure out how it’s useful, you’ll find remarkable utility waiting. It’s ok, man. I’m sure many folks found the computer useless too.
> Explain when pin is important in rust when dealing with asynchronous code, particularly when dealing with Box<dyn> types.
In Rust, Pin is a concept that is central to understanding the implementation of asynchronous operations. To explain why, let's first cover the basics.
Asynchronous tasks often involve future types that encapsulate a computation that will produce a value at some point in the future. These futures may need to poll other futures, which in turn might not be ready, causing them to be suspended and resumed later on. This suspension and resumption is where the Pin concept comes in.
By default, Rust allows moving types around in memory. However, when you have self-referential structures, like many of the future types in asynchronous programming, this can lead to problems. A future may hold a reference to another part of itself, and if the future is moved in memory, that internal reference may become invalid.
Pin is Rust's solution to this problem. If a type is "pinned" (wrapped in a Pin), it is a guarantee that the memory location of the value inside will not change. This means that you can safely keep references to different parts of the same structure because you know they won't move around.
Box<dyn Future> is a heap-allocated future object. Using Pin with Box<dyn Future> (i.e., Pin<Box<dyn Future>>) is common in async code because it guarantees that the future object will not be moved around in memory, making it safe to poll.
However, one should note that simply creating a Pin<Box<T>> does not mean that the T will stay put; it's also necessary to ensure that T does not move itself or its interior around. The contract of Pin is such that, once a value has been pinned, it is not allowed to move or have its memory invalidated until it is dropped. For a type to uphold these guarantees, it must be Unpin or ensure that all its operations maintain these guarantees. Most native Rust types are Unpin and therefore don't need to worry about these guarantees.
In short, Pin is important in Rust's async code as it provides a mechanism to safely handle self-referential structures, which are common in async programming. The Rust async ecosystem uses Pin to ensure that once a future begins executing (is polled), it will remain at a fixed location in memory until it has completed.
> If a type is "pinned" (wrapped in a Pin), it is a guarantee that the memory location of the value inside will not change.
Pin is a wrapper around a pointer type and disallows moving the value that that pointer points at. You don’t pin a value, you pin a reference to a value. IMHO this sentence is unclear about that.
You sorta get the right vibes from the rest of the post, but there’s a major important concept in here it explains decently but also just wrong enough that you may internalize the incorrect thing.
I agree - it’s not a panacea devoid of human involvement. I think really importantly, whatever failings the technique has, it’s reflective of humanity itself, and humans are often slightly wrong or misleading. I think confusing it’s output with that of a deterministic program is wrong - it’s much more akin to the output of a human than not.
My argument though is it’s not a freshman in college level of human failings. It’s clarity is far beyond that on many subjects, and it’s facility to “understand” is remarkable for a human let alone a computer. The fact I can interrogate it and ask it the clarifying question you bring out is beyond useful - I can dig into the specific areas of confusion I have, and often if it’s wrong I’ll cop to it unlike a human oracle.
> Clarify then: If a type is "pinned" (wrapped in a Pin), it is a guarantee that the memory location of the value inside will not change.
When we say "the memory location of the value inside will not change," what we mean is that the value that the pointer points to is guaranteed to not move in memory. This is a critical guarantee when working with certain types of data, like self-referential structs or certain async code in Rust.
Let's take an example of Pin<Box<T>>. Here's what it means:
Box<T>: This is a heap-allocated instance of T. The Box is a smart pointer that points to this heap-allocated T. Pin<Box<T>>: This is a Pin wrapping the Box. This means that the T that the Box points to is pinned. This does not mean that the Box itself cannot be moved. The Box is a pointer, and pointers can be copied and moved freely. But because we have used Pin, the actual heap-allocated T that it points to cannot be moved. This is what we mean when we say "the memory location of the value inside will not change." We're talking about the T, not the Box.
This is important when the type T has self-references, because moving T in memory would invalidate those self-references. By using Pin, we ensure that T stays put, and those self-references remain valid. This is a key part of the design of Rust's async programming model.
However, this guarantee is only upheld as long as the type T does not implement Unpin, which is a marker trait that indicates that it is safe to move a type out of a Pin. Types that are not Unpin uphold the guarantee that they cannot be moved out of the Pin once they are placed in it.
Absolutely, and I don't think every explanation has to be perfect to be useful, hence me saying "you gotta watch out" and not "fuck this tool, nobody should use it."
But I have found asking questions like "how would I ..?" or "explain ..?" can be useful as long as you don't treat like a final answer.
Programming is one of the fields were correctness actually matters in a binary way. But jobs where "sort of" or 80% is good enough can be replaced with language models.
^ Your citation, sir.
I will say that checking back a day later, I am stunned at how many smart programmer types are clearly not even close to getting how useful this tool is. For people that don't find it very helpful, to me that just means they're not asking enough of it yet. More people just need to spring for the $20/month and start asking GPT4 about any old technical subject they think they know well but about which they might also have holes in their knowledge.
It's a tool that rewards creativity, so you kind of get out what you put in. Many folks here are too young, but back when search engines were coming out, there was a phase for many people where they only knew how to treat it as a toy. Like, search for their own web page to see if it showed up; search for a question they already knew an answer to to see if it was correct. It required a bit of a mental reset; a "click"; before each person would know automatically, without reminding themselves, that they could actually search for things they didn't know.
It seems like there is something similar going on here. It's not a search engine so it's not exactly about stuff we do or don't know, but I gather that a lot of people thus far have not uncovered the advantages it actually gives them.
Citation needed. My day to day has not changed one bit, even if I'm using Copilot and ChatGPT. I get marginally faster autocomplete and a buggy template engine. This type of comment is exactly what GP means when they say "grossly overestimated."