lifetime

问题 Rust disallows this kind of code because it is unsafe: fn main() { let mut i = 42; let ref_to_i_1 = unsafe { &mut *(&mut i as *mut i32) }; let ref_to_i_2 = unsafe { &mut *(&mut i as *mut i32) }; *ref_to_i_1 = 1; *ref_to_i_2 = 2; } How can I do do something bad ( e.g. segmentation fault, undefined behavior, etc.) with multiple mutable references to the same thing? The only possible issues I can see come from the lifetime of the data. Here, if i is alive, each mutable reference to it should be

问题 I am writing a function of the following format: fn pop(data: &mut Vec<Option<T>>) -> Option<T> { // Let the item be the current element at head let item = data[0]; // and "remove" it. data[0] = None; item } When I try to do this, I get a "cannot move out of indexed content" error, which makes sense. When I try to change it such that item is a reference, I get an error when I try to set data[0] to None , which also makes sense. Is there some way I can do what I want to do? It seems to me that

问题 This should be a simple question but I haven't managed to find the answer on google. I would like to know, in terms an idiot can understand, exactly what application lifetime means in ASP.NET (and therefore when you can expect application start and end events to run). I assumed it would be when you run and stop the app in IIS, but I've read things that suggest it's related to number of requests. 回答1: By default the lifetime starts with the first request to the app. And it ends after an idle

问题 Given the following code: class foo { }; class bar: public foo { public: ~bar() { printf("~bar()\n"); } }; class zab: public foo { public: ~zab() { printf("~zab()\n"); } }; struct foo_holder { const foo &f; }; int main() { foo_holder holder[]= { {bar()}, {zab()} }; printf("done!\n"); return 0; } the output is: ~bar() ~zab() done! C++0x has a clause that dictates this can create dangling references when used as a new initializer, but it says nothing (at least nothing I can find) about

问题 How are lifetimes handled when there is a trait object passed to a function? struct Planet<T> { i: T, } trait Spinner<T> { fn spin(&self, value: T); } impl<T> Spinner<T> for Planet<T> { fn spin(&self, value: T) {} } // foo2 fails: Due to lifetime of local variable being less than 'a fn foo2<'a>(t: &'a Spinner<&'a i32>) { let x: i32 = 10; t.spin(&x); } // foo1 passes: But here also the lifetime of local variable is less than 'a? fn foo1<'a>(t: &'a Planet<&'a i32>) { let x: i32 = 10; t.spin(&x)

问题 In Rust, I get the following error: <anon>:14:9: 14:17 error: `mystruct` does not live long enough <anon>:14 mystruct.update(); ^~~~~~~~ <anon>:10:5: 17:6 note: reference must be valid for the lifetime 'a as defined on the block at 10:4... <anon>:10 { <anon>:11 let initial = vec![Box::new(1), Box::new(2)]; <anon>:12 let mystruct = MyStruct { v : initial, p : &arg }; <anon>:13 <anon>:14 mystruct.update(); <anon>:15 ... <anon>:12:59: 17:6 note: ...but borrowed value is only valid for the block

问题 The "undead" clause I call the undead clause the C++ rule that after the destruction of an object, if a new object is created at the same address, it can sometimes be considered the same object as the old one. That rule always existed in C++ but with some changes on the additional conditions. I was made to read the latest undead clause by this question. The revised conditions in Lifetime [basic.life]/8 are: (8.1) the storage for the new object exactly overlays the storage location which the

问题 The 12.2.5 section of standard says: A temporary bound to a reference parameter in a function call (5.2.2) persists until the completion of the full expression containing the call. A temporary bound to the returned value in a function return statement (6.6.3) persists until the function exits. In all these cases, the temporaries created during the evaluation of the expression initializing the reference, except the temporary to which the reference is bound, are destroyed at the end of the full

问题 This is the minimal code: struct Node<T> { item: T, next: Link<T>, } type Link<T> = Option<Box<Node<T>>>; pub struct IterMut<'a, T>(&'a mut Link<T>); impl<'a, T> Iterator for IterMut<'a, T> { type Item = &'a mut T; fn next(&mut self) -> Option<Self::Item> { self.0.as_mut().map(|boxed_node| { self.0 = &mut boxed_node.next; &mut boxed_node.item }) } } As far as I understand, there should be no problem. I have done a lot of searching, but no way. error[E0495]: cannot infer an appropriate

问题 I'm building a PromptSet that can ask a series of questions in a row. For testing reasons, it allows you to pass a reader and writer instead of using stdin & stdout directly. Because stdin and stdout are the common use case, I would like to create a default "constructor" that allows the user to produce a PromptSet<StdinLock, StdoutLock> without needing any parameters. Here's the code so far: use std::io::{self, BufRead, StdinLock, StdoutLock, Write}; pub struct PromptSet<R, W> where R: