reference

问题 I'm a new Rust user and I'm reading a book The Complete Rust Programming Reference Guide . In the book there is an example: fn main() { let mut a = String::from("testing"); let a_ref = &mut a; a_ref.push('!'); println!("{}", a); } The book states the code will generate an error. However, on my local machine, I can run it without any issue. Is this because I'm using a newer Rust compiler [ rustc 1.41.0-nightly (412f43ac5 2019-11-24) ] and the code doesn't work on older ones? I've read some

问题 Say I have got some function fun , the actual code body of which is out of my control. I can create a new function which does some preprocessing before calling fun , i.e. def process(x): x += 1 return fun(x) If I now want process to take the place of fun for all future calls to fun , I need to do something like # Does not work fun = process This does not work however, as this creates a cyclic reference problem as now fun is called from within the body of fun . One solution I have found is to

问题 I am trying to understand why the following code fails: fn main() { let mut a = 10; let mut b = 20; let mut c = 30; let p = vec![&mut a, &mut b, &mut c]; // works with [&a, &b, &c] for &x in &p { // works with 'x' instead of of '&x' println!("{}", x); } } The error message is: error[E0507]: cannot move out of borrowed content --> src/main.rs:7:9 | 7 | for &x in &p { | ^- | || | |hint: to prevent move, use `ref x` or `ref mut x` | cannot move out of borrowed content As I understand, the

问题 At the moment I'm working on an application that has to use a connection factory. When I lookup the connection factory directly on a global level by the name set in WAS everything is working fine, but for means of decoupling I want to define a resource reference in my application and lookup that name. So I created following entry in my application.xml: <resource-ref> <res-ref-name>jms/connectionFactory</res-ref-name> <res-type>javax.jms.ConnectionFactory</res-type> <res-auth>Container</res

问题 It seems that when I pass different integers directly to a function, C++ assigns them the same address as opposed to assigning different addresses to different values. Is this by design, or an optimization that can be turned off? See the code below for an illustration. #include <iostream> const int *funct(const int &x) { return &x; } int main() { int a = 3, b = 4; // different addresses std::cout << funct(a) << std::endl; std::cout << funct(b) << std::endl; // same address std::cout << funct

问题 I get an error when I include a header file, but not if I include the source file instead. The function is defined in the source file like this: /* in User.c */ struct User { const char* name; }; struct User* addedUser(const char* name) { struct User* user = malloc(sizeof(struct User)); user->name = name; return user; } And used like this: /* in main.c */ int test_addedUser() { char* newName = "Fooface"; struct User* newUser = addedUser(newName); assert(!strcmp(newName, newUser->name));

问题 I have the following use-case I try to solve with JSON schemas. I have a generic JSON data schema for, for example, a user. Here is an example of the user.schema.json file. { "type": "object", "definitions": {}, "$schema": "http://json-schema.org/draft-07/schema#", "properties": { "name": { "type": "string", "minLength": 1 }, "email": { "type": "string", "minLength": 1 }, "locale": { "type": "string", "minLength": 1 }, "active": { "type": "boolean", "default": true }, "password": { "type":

问题 I cannot find any definition for invalidation of pointers/references in the Standard. I ask because I just found out that C++11 forbids copy-on-write (COW) for strings. As far as I understand, if COW was applied then p would be still a valid pointer and r a valid reference after the following commands: std::string s("abc"); std::string s2(s); char * p = &(s2[0]); char & r = s2[0]; s2[1] = "B"; Just they would no longer point/refer to the first character of s2 , but merely to the first

问题 Certain types in Go are reference types: maps, slices, channels, functions, and methods. Sometimes you need to use pointers to references. For example, type Stack []interface{} func (stack *Stack) Push(x interface{}) { *stack = append(*stack, x) } You need it because all arguments are passed by copying the value, and append() might need to reallocate memory in the slice's capacity is not big enough. I get that. First question. How about map types? If I have a custom type based on a map ,

问题 Certain types in Go are reference types: maps, slices, channels, functions, and methods. Sometimes you need to use pointers to references. For example, type Stack []interface{} func (stack *Stack) Push(x interface{}) { *stack = append(*stack, x) } You need it because all arguments are passed by copying the value, and append() might need to reallocate memory in the slice's capacity is not big enough. I get that. First question. How about map types? If I have a custom type based on a map ,