在 rust 中加入一个字符串向量

Question

I want to join a string vector into a String , but I got confused on the different result of vector of &str &String String :

let v1: Vec<String> = vec!["foo".to_string(), "bar".to_string()];
println!("{:?}", v1.join(",")); // OK

let v2: Vec<&str> = vec!["foo", "bar"];
println!("{:?}", v2.join(",")); // OK

let foo = "foo".to_string();
let bar = "bar".to_string();
let v3: Vec<&String> = vec![&foo, &bar];
println!("{:?}", v3.join(",")); // error

Here's the error:

error[E0599]: no method named `join` found for type `std::vec::Vec<&std::string::String>` in the current scope
  --> src/main.rs:11:21
   |
11 | println!("{:?}", v3.join(",")); // error
   |                     ^^^^ method not found in `std::vec::Vec<&std::string::String>`

Any help and explanation is really welcome

Answer 1

In general, using a &String is discouraged: if you need an owned copy, use a String and if you need a reference, use an &str . Automatic dereferencing allows this to be reasonably transparent:

let foo: String = "foo".to_string();
let bar: String = "bar".to_string();
let v3: Vec<&str> = vec![&foo, &bar];

Note: In the above code, you don't really need to write the types explicitly, but I put them in to show that a Vec<&str> can be built transparently from references to variables of type String .