strfmt doesn't work with literal strings as keys

[acjay]

I might be doing something wrong, but it appears that strfmt doesn't accept a HashMap with keys that are string literals (i.e. &'static str). This seems weird to me, as this seems like a common situation.

I would naively expect the following to work:

use std::collections::HashMap;
use strfmt::strfmt;

fn main() {
    let mut params: HashMap<&str, &str> = HashMap::new();
    params.insert("word1", "hello");
    params.insert("word2", "world");

    println!("{}", strfmt("{word1} {word2}", &params).unwrap());
}

But it fails to compile, with the following error:

error[E0277]: the trait bound `&str: FromStr` is not satisfied
  --> src/main.rs:9:46
   |
9  |     println!("{}", strfmt("{word1} {word2}", &params).unwrap());
   |                    ------                    ^^^^^^^ the trait `FromStr` is not implemented for `&str`
   |                    |
   |                    required by a bound introduced by this call
   |
   = help: the trait `FromStr` is implemented for `String`
note: required by a bound in `strfmt`
  --> /Users/alanjohnson/.cargo/registry/src/index.crates.io-6f17d22bba15001f/strfmt-0.2.4/src/lib.rs:55:20
   |
53 | pub fn strfmt<'a, K, T: DisplayStr>(fmtstr: &str, vars: &HashMap<K, T>) -> Result<String>
   |        ------ required by a bound in this function
54 | where
55 |     K: Hash + Eq + FromStr,
   |                    ^^^^^^^ required by this bound in `strfmt`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `strfmt_test` (bin "strfmt_test") due to 1 previous error

One fix is to explicit convert the string literals to String:

use std::collections::HashMap;
use strfmt::strfmt;

fn main() {
    let mut params: HashMap<String, &str> = HashMap::new();
    params.insert("word1".to_string(), "hello");
    params.insert("word2".to_string(), "world");

    println!("{}", strfmt("{word1} {word2}", &params).unwrap());
}

This seems kinda weird to me, because I would think this is a common use case and that there wouldn't be a need to add the boilerplate of string conversions.

[vitiral]

It is a common situation. It's the exact situation that std::fmt already supports!

[vitiral]

if you have static strings, then just do format!("x = {}, y = {val}", 10, val = 30);

[acjay]

That only works if you have a literal string for the format. I didn't demonstrate this in my example, but the reason I'm trying to do this is because I want to have the format string reside in a constant in a different module.

[vitiral]

Yes, that use-case isn't supported by this library.

In theory I suppose it could support AsRef<str> keys and values. I'd be willing to accept a PR which did that.