How to access struct properties dynamically? - rust

Question

I am a Rust beginner and was wondering how to access a struct's fields dynamically:
use std::collections::HashMap;
struct User {
email: String,
name: String,
}
impl User {
fn new(attributes: &HashMap<String,String>) -> User {
let mut model = User {
email: "",
name: "",
};
for (attr_name,attr_value) in attributes {
// assign value "attr_value" to attribute "attr_name"
// no glue how to do this
// in php would be: $model->{$attr_name} = $attr_value;
model.*attr_name *= attr_value;
}
model;
}
}
fn main() {
let mut map: HashMap::new();
map.insert("email",String::from("foo#bar.de"));
map.insert("name",String::from("John doe"));
user_model = User::new(&map);
println!("{:?}",user_model);
}
How it is possible to initialize a struct by given HashMap?

Answer 1

Unless you change your User to contain a HashMap then Rust can't do that kind of "magic" (or it will require some proc macro usage, which is not beginner friendly).
Instead you can use a match, and match all the keys and update the User fields:
for (attr_name, attr_value) in attributes {
match attr_name {
"email" => model.email = attr_value.clone(),
"name" => model.name = attr_value.clone(),
_ => {}
}
}
However, instead of having empty Strings, I'd suggest using Option<String>.
struct User {
email: Option<String>,
name: Option<String>,
}
Then you can simplify your whole new method to just:
fn new(attributes: &HashMap<String, String>) -> User {
User {
email: attributes.get("email").cloned(),
name: attributes.get("name").cloned(),
}
}
Since you have some mixed String and &'static str usage, along with Debug not being implemented. Then here is the complete example:
use std::collections::HashMap;
#[derive(Debug)]
struct User {
email: Option<String>,
name: Option<String>,
}
impl User {
fn new(attributes: &HashMap<String, String>) -> User {
User {
email: attributes.get("email").cloned(),
name: attributes.get("name").cloned(),
}
}
}
fn main() {
let mut map = HashMap::new();
map.insert(String::from("email"), String::from("foo#bar.de"));
map.insert(String::from("name"), String::from("John doe"));
let user_model = User::new(&map);
println!("{:?}", user_model);
}