Rust best practices when specifying a constant hash map

Question

I'm trying to set a constant, predefined hash map in Rust. I'm not sure what the best practice is in Rust for this.

use std::collections::HashMap;

pub const Countries: HashMap<&str, &str> = [
    ("UK", "United Kingdom"),
    ("US", "United States")
].iter().cloned().collect();

These will then be referenced later in the library.

If this is bad, I'm guessing a match in a function is the best way?

i used something similar lately (together with [`lazy_static`](https://docs.rs/lazy_static/1.2.0/lazy_static/); there is even a `HashMap` example in the doc). interested to see what people will suggest here. — hiro protagonist, Feb 18 '20 at 06:26

Martin Gallagher · Accepted Answer · 2020-03-20T13:40:32.563

58

You can use https://crates.io/crates/lazy_static (lazily executed at runtime).

I personally use https://crates.io/crates/phf (compile-time static collections) for this if the data is truly static.

use phf::{phf_map};

static COUNTRIES: phf::Map<&'static str, &'static str> = phf_map! {
    "US" => "United States",
    "UK" => "United Kingdom",
};

edited Mar 20 '20 at 13:40

answered Feb 18 '20 at 07:02

Martin Gallagher

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5

phf is great, thank you. Add it with `cargo add phf --features macros` – jnnnnn Aug 15 '22 at 05:42

Rust best practices when specifying a constant hash map

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