存储任何类型的物体在生锈中
我想实现一个可以存储任何类型的对象的class 存储。我正在尝试使用特质任何来做到这一点。 存储:: insert ::＆lt; t＆gt;（键，value）应添加一对，其中键始终是某些string类型，并且该值可以是任何类型。当我存储一个box＆lt; hashmap＆lt; string，dyn any ny＆gt;＆gt;编译器说它在编译时没有大小。那么如何避免该错误呢？
use std::any::{Any, TypeId};
use std::collections::hash_map::Keys;
use std::collections::HashMap;
pub struct Storage where Self: Sized{
map: Box<HashMap<String, dyn Any>>,
}
impl Storage {
pub fn new() -> Self {
Self {
map: Some(Box::new(HashMap::new())),
}
}
pub fn insert<Q: Any>(&mut self, key: &dyn Any, obj: Q) {
if key.is::<String>() {
let key_string = key.downcast_ref::<String>().unwrap();
self.map.as_mut().insert(key_string.clone(), obj);
}
}
}
另外，我不确定是否可以使用std :: Collections :: Hashmap实现此类类
I want to implement a class Storage that can store objects of any types. I am trying to do that using trait Any. The Storage::insert::<T>(key, value) should add a pair, where the key is always some String type, and the value can be any type. When I store a Box<HashMap<String, dyn Any>> the compiler says that it doesn't have size at compile-time. So how can I avoid that error ?
use std::any::{Any, TypeId};
use std::collections::hash_map::Keys;
use std::collections::HashMap;
pub struct Storage where Self: Sized{
map: Box<HashMap<String, dyn Any>>,
}
impl Storage {
pub fn new() -> Self {
Self {
map: Some(Box::new(HashMap::new())),
}
}
pub fn insert<Q: Any>(&mut self, key: &dyn Any, obj: Q) {
if key.is::<String>() {
let key_string = key.downcast_ref::<String>().unwrap();
self.map.as_mut().insert(key_string.clone(), obj);
}
}
}
Also I'm not sure that such class can be implemented with std::collections::HashMap
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问题是
haspmap＆lt; k，v＆gt;需要具有大小类型 k k 和v，这不是dyn的情况Any。这意味着必须在编译时知道k和v的大小。例如，您始终知道u32将需要32位，但是[u32]的大小事先未知。因此：u32：大小和[u32]：！大小。dyn any，dyn any也是如此：！大小，因为不同大小的对象可以实现任何，实际上，实际上， 每个对象实现任何。为了解决这个问题，有一个简单的补丁，它将该类型用
box＆lt; _＆gt;包装。box是指向堆分配的内存的指针，因此您知道它的大小将始终是指针的大小（粗略地说），并且您无需在编译时知道多少内存您将在堆上分配。在这里：您还必须调整其余的代码，但是您可以找到所有内容 。
The problem is that
HaspMap<K, V>needs to haveSizedtypesKandV, which is not the case ofdyn Any. This means that the size ofKandVmust be known at compile time. For instance, you always know that anu32will take 32 bits, but the size of[u32]is not known beforehand. Therefore:u32: Sized, and[u32]: !Sized.This is also the case of
dyn Any,dyn Any: !Sized, because objects of different size can implementAny, and, in fact, every object implementsAny.To solve this, there is an easy patch, and it's wrapping that type with
Box<_>.Boxis a pointer to a heap-allocated memory, so you know its size will always be the size of a pointer (roughly speaking), and you don't need to know at compile time how much memory you will allocate on the heap. Here it goes:You will also have to adapt the rest of the code, but you can find everything in the documentation.