CODEWITHSUNDEEP
jsonrust
Incerteza
Incerteza

Reputation: 34924

TreeMap<String, String> to json

I have the following code:

extern crate serialize;

use std::collections::TreeMap;
use serialize::json;
use serialize::json::ToJson;
use serialize::json::Json;

fn main() {
  let mut tree_map = get_tree_map(); // : TreeMap<String, String>

  let mut tree_map2 = tree_map.iter().map(|k, v| (k, v.to_json())); //error the type of this value must be known in this context
  let json1 = json::Object(tree_map2);
}

I want to convert tree_map to json. I tried to do it by converting it to TreeMap<String, Json> but failed. How can I do that?

Upvotes: 1

Views: 422

Answers (1)

Francis Gagn&#233;
Francis Gagn&#233;

Reputation: 65822

The closure you passed to map takes two parameters, but it should take a single parameter that is a tuple type, because iter() returns an iterator over tuples (see Trait Implementations on Entries). Change |k, v| to |(k, v)| to fix this. (I found this by adding explicit type annotations on k, v: the compiler then complained about the closure not having the right number of parameters.)

There are some other errors however. Instead of using iter(), you might want to use into_iter() to avoid cloning the Strings if you don't need the TreeMap<String, String> anymore. Also, you should add .collect() after .map(...) to turn the iterator into a TreeMap. The compiler will automatically infer the type for tree_map2 based on the requirements for json::Object.

fn main() {
  let mut tree_map = get_tree_map(); // : TreeMap<String, String>

  let mut tree_map2 = tree_map.into_iter().map(|(k, v)| (k, v.to_json())).collect();
  let json1 = Json::Object(tree_map2);
}

Upvotes: 2

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