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I hop into Rust beginners from time to time, but it's usually pretty empty so a bit hard to get an answer. I'm very likely explaining the problem incorrectly, s

I hop into Rust beginners from time to time, but it's usually pretty empty so a bit hard to get an answer. I'm very likely explaining the problem incorrectly, so let me give you an example: https://gist.github.com/anonymous/3d72907031ce18d002364e756f6c0346 https://gist.github.com/anonymous/3d72907031ce18d002364e756f... As you can expect, line 13 is trying to borrow a value that does not live long enough for `req`. Unfortunately, hyper::client::Client's req.body() requires a &str it seems. Somehow i need to pass it a &str (which i would normally do via &String). Do i need to move s:String out of the block? Do i need to specify a lifetime? These are the sort of "What do i even search for!?" moments i run into heh. Granted, less so these days.. thankfully. Note that `&mut Some(ref c)` looks pretty terrible, i'm experimenting with an API i'm writing.

steveklabnik 10y ago
I try to idle in there during NYC 9-5ish at least, but depending on your time zone, it can be tough. Without compiling myself, it can be a bit tricky, but... Yes, so the issue here is, your String will go out of scope at the end if the if let, on 14. But you're trying to store a reference to it in something that lives longer: the req will continue to live afterwards. So yes, you need to move s outside of the block somehow; there are a few different ways of doing this. What I'd try first is something like this: https://gist.github.com/steveklabnik/54cf7a4a522cd1a7c6e0130760903b75 https://gist.github.com/steveklabnik/54cf7a4a522cd1a7c6e0130... Now that the binding lives in the outer scope, it will live longer than the `if let`, you're basically moving it out. I'm trusting the compiler's control flow analysis here; it should let you do this, given that you only use s after you've assigned to it.
- fizzbatter 10y ago
  Indeed, that worked! So, it's good to know i had the right idea (moving the data out of the block), but i didn't think to store it above the request body. I was trying to be clever, and use explicitly say that `s` should live for the lifetime of the parent function. Any idea if that is possible in this case? edit: Sidenote, i appreciate that you hang in Rust Beginners, i didn't mean to imply that people weren't being helpful. Just that, it can be difficult to find a solution at times. On the plus side, i managed to help (i hope haha) a guy in #rust-beginners today, so hopefully i've paid it forward a bit. Appreciate your help!
  - steveklabnik 10y ago
    Yeah no worries :) > Any idea if that is possible in this case? This is what I meant by liftimes being descriptive, not prescriptive: you can't add an annotation and make something live longer. Moving the binding itself is the only way.
openasocket 10y ago
OK, I see what the problem is. This is the type signature for the body method: fn body<B: Into<Body<'a>>>(self, body: B) -> RequestBuilder<'a> The RequestBuilder struct tries to be clever: it just keeps a pointer to what you want the body to be rather than taking ownership of it or copying it. So when you say that "req = req.body(&s)" you've given the request a pointer to your string, but that string is freed inside that if-block. I don't see an obvious fix right now, but I'll update this is I see something.
- fizzbatter 10y ago
  Yea, that's another thing about rust. At times, things like what Hyper's Body method is doing can be quite puzzling. And while Rust's attempt to help is noble, it can end up even more confusing. At times it is awesome, but it can be a lot of visual noise for beginners. Fwiw, https://news.ycombinator.com/item?id=11780196 https://news.ycombinator.com/item?id=11780196 has the answer to my example problem. I'm also inquiring about using lifetimes to solve the problem.

steveklabnik 10y ago

I try to idle in there during NYC 9-5ish at least, but depending on your time zone, it can be tough. Without compiling myself, it can be a bit tricky, but... Yes, so the issue here is, your String will go out of scope at the end if the if let, on 14. But you're trying to store a reference to it in something that lives longer: the req will continue to live afterwards. So yes, you need to move s outside of the block somehow; there are a few different ways of doing this. What I'd try first is something like this: https://gist.github.com/steveklabnik/54cf7a4a522cd1a7c6e0130760903b75 https://gist.github.com/steveklabnik/54cf7a4a522cd1a7c6e0130... Now that the binding lives in the outer scope, it will live longer than the `if let`, you're basically moving it out. I'm trusting the compiler's control flow analysis here; it should let you do this, given that you only use s after you've assigned to it.

fizzbatter 10y ago
Indeed, that worked! So, it's good to know i had the right idea (moving the data out of the block), but i didn't think to store it above the request body. I was trying to be clever, and use explicitly say that `s` should live for the lifetime of the parent function. Any idea if that is possible in this case? edit: Sidenote, i appreciate that you hang in Rust Beginners, i didn't mean to imply that people weren't being helpful. Just that, it can be difficult to find a solution at times. On the plus side, i managed to help (i hope haha) a guy in #rust-beginners today, so hopefully i've paid it forward a bit. Appreciate your help!
- steveklabnik 10y ago
  Yeah no worries :) > Any idea if that is possible in this case? This is what I meant by liftimes being descriptive, not prescriptive: you can't add an annotation and make something live longer. Moving the binding itself is the only way.

openasocket 10y ago

OK, I see what the problem is. This is the type signature for the body method: fn body<B: Into<Body<'a>>>(self, body: B) -> RequestBuilder<'a> The RequestBuilder struct tries to be clever: it just keeps a pointer to what you want the body to be rather than taking ownership of it or copying it. So when you say that "req = req.body(&s)" you've given the request a pointer to your string, but that string is freed inside that if-block. I don't see an obvious fix right now, but I'll update this is I see something.

fizzbatter 10y ago
Yea, that's another thing about rust. At times, things like what Hyper's Body method is doing can be quite puzzling. And while Rust's attempt to help is noble, it can end up even more confusing. At times it is awesome, but it can be a lot of visual noise for beginners. Fwiw, https://news.ycombinator.com/item?id=11780196 https://news.ycombinator.com/item?id=11780196 has the answer to my example problem. I'm also inquiring about using lifetimes to solve the problem.