How to make a compiled Regexp a global variable?

Question

I have several regular expressions that are defined at runtime and I would like to make them global variables.

To give you an idea, the following code works:

use regex::Regex; // 1.1.5

fn main() {
    let RE = Regex::new(r"hello (\w+)!").unwrap();
    let text = "hello bob!\nhello sue!\nhello world!\n";
    for cap in RE.captures_iter(text) {
        println!("your name is: {}", &cap[1]);
    }
}

But I would like it to be something like this:

use regex::Regex; // 1.1.5

static RE: Regex = Regex::new(r"hello (\w+)!").unwrap();

fn main() {
    let text = "hello bob!\nhello sue!\nhello world!\n";
    for cap in RE.captures_iter(text) {
        println!("your name is: {}", &cap[1]);
    }
}

However, I get the following error:

error[E0015]: calls in statics are limited to constant functions, tuple structs and tuple variants
 --> src/main.rs:3:20
  |
3 | static RE: Regex = Regex::new(r"hello (\w+)!").unwrap();
  |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^

Does this mean that I need nightly Rust in order to make these variables global, or is there another way to do it?

Answer 1

You can use the lazy_static macro like this:

use lazy_static::lazy_static; // 1.3.0
use regex::Regex; // 1.1.5

lazy_static! {
    static ref RE: Regex = Regex::new(r"hello (\w+)!").unwrap();
}

fn main() {
    let text = "hello bob!\nhello sue!\nhello world!\n";
    for cap in RE.captures_iter(text) {
        println!("your name is: {}", &cap[1]);
    }
}

If you are using the 2015 edition of Rust, you can still use lazy_static via:

#[macro_use]
extern crate lazy_static;