How to access struct properties dynamically?

user_2215332 0
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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?

rust
1 Answers

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);
}
user_24708180
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