How can I define Rust structure literals similar to Python's?-CodePudding

I want to initialize a Rust variable with a literal.

Shepmaster guesses that Rust has no map literal because:

the fact that there are multiple data structures that act maplike (such as both BTreeMap and HashMap) would make it hard to pick one.

But Rust says "you should probably just use Vec or HashMap", meaning that if they are good enough for most purposes, then using them when initializing from a literal value should usually work just fine.

The example map initialization is clumsy, but printing it produces a more concise representation:

{"Mars": 1.5, "Mercury": 0.4, "Earth": 1.0, "Venus": 0.7}.

fn main() {
use std::collections::HashMap;

let solar_distance = HashMap::from([
    ("Mercury", 0.4),
    ("Venus", 0.7),
    ("Earth", 1.0),
    ("Mars", 1.5),
]);

println!("{:?}", solar_distance)
}

In Python x = {"Mars": 1.5, "Mercury": 0.4, "Earth": 1.0, "Venus": 0.7} would initialize a dict variable. It would be nice if a future version of Rust would accept nested list and map literals to initialize the corresponding default Vec and HashMap structures.

Is a concise nested literal format on the Rust feature roadmap?

A second-best solution would initialize structures from a JSON string (perhaps with some syntactic sugar to avoid quote-escape hell):

fn main() {
use std::collections::HashMap;

let x = String::from("{'Venus': 0.7, 'Mars': 1.5, 'Mercury': 0.4, 'Earth': 1.0}");
println!("{:?}", x);

let solar_distance = HashMap::from(x);
println!("{:?}", solar_distance);
}

But this fails with:

    |
7   | let solar_distance = HashMap::from(x);
    |                      ^^^^^^^^^^^^^ the trait `From<String>` is not implemented for `HashMap<_, _, _>`

Has anyone written a method to initialize a nested vec/hash variable from a JSON string?

CodePudding user response：

If you want to be able to initialize a HashMap concisely (similar to vec![]), take a look at https://crates.io/crates/hmap. It does basically exactly what you're describing.

If you want to work with serde_json, you can use the json!() macro provided by that library:

let x = json!({
  "foo": "bar",
  "baz": [1, 2, 3],
});