How to create a static array of strings?

Question

Note This question contains syntax that predates Rust 1.0. The code is invalid, but the concepts are still relevant.

How do you create a global static array of strings in Rust?

For integers, this compiles:

static ONE:u8 = 1;
static TWO:u8 = 2;
static ONETWO:[&'static u8, ..2] = [&ONE, &TWO];

But I can't get something similar for strings to compile:

static STRHELLO:&'static str = "Hello";
static STRWORLD:&'static str = "World";
static ARR:[&'static str, ..2] = [STRHELLO,STRWORLD]; // Error: Cannot refer to the interior of another static

This code in the rust playpen: is.gd/IPkdU4

Andrew Wagner
– Andrew Wagner

2014-12-13 14:18:37 +00:00
Commented Dec 13, 2014 at 14:18 — Andrew Wagner
– Andrew Wagner, Commented Dec 13, 2014 at 14:18

Shepmaster · Accepted Answer · 2017-01-30 03:20:18Z

111

This is a stable alternative for Rust 1.0 and every subsequent version:

const BROWSERS: &'static [&'static str] = &["firefox", "chrome"];

edited Jan 30, 2017 at 3:20

Shepmaster

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answered Sep 3, 2015 at 19:23

Quartz

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1 Comment

Felix D. Over a year ago

You can drop the 'static lifetime specifiers const BROWSERS: &[&str] = &["firefox", "chrome"];

jcroskery · Accepted Answer · 2019-08-11 07:35:58Z

8

There are two related concepts and keywords in Rust: const and static:

https://doc.rust-lang.org/reference/items/constant-items.html

For most use cases, including this one, const is more appropriate, since mutation is not allowed, and the compiler may inline const items.

const STRHELLO:&'static str = "Hello";
const STRWORLD:&'static str = "World";
const ARR:[&'static str, ..2] = [STRHELLO,STRWORLD];

Note, there is some out-of-date documentation out there that doesn't mention the newer const, including Rust by Example.

edited Aug 11, 2019 at 7:35

jcroskery

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answered Dec 13, 2014 at 14:54

Andrew Wagner

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2 Comments

Mattias Bengtsson Over a year ago

The documentation moved to a new place.

Jeremy Meng Over a year ago

There is a typo in the example code, the first , should have been ; as in const ARR:[&'static str; ..2] = [STRHELLO,STRWORLD];

Adrian · Accepted Answer · 2017-01-30 02:28:14Z

6

Another way to do it nowadays is:

const A: &'static str = "Apples";
const B: &'static str = "Oranges";
const AB: [&'static str; 2] = [A, B]; // or ["Apples", "Oranges"]

answered Jan 30, 2017 at 2:28

Adrian

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2 Comments

typically Over a year ago

Is there a way to have the compiler infer the length (2) from the number of elements listed?

BallpointBen Over a year ago

@nishanthshanmugham Unstable github.com/rust-lang/rust/issues/85077 #![feature(generic_arg_infer)]

Eduardo Pereira · Accepted Answer · 2023-03-12 12:38:47Z

Just used this to allocate a small POC level for a game in Rust

const LEVEL_0: &'static [&'static [i32]] = &[
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 9, 0, 0, 0, 2, 0, 0, 3, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
    &[1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
];

And loaded using the following function

pub fn load_stage(&mut self, ctx: &mut Context, level: usize) {
    let levels = vec![LEVEL_0];

    for (i, row) in levels[level].iter().enumerate() {
        for (j, col) in row.iter().enumerate() {
            if *col == 1 {
                self.board.add_block(
                    ctx,
                    Vector2::<f32>::new(j as f32, i as f32),
                    self.cell_size,
                );
            }

Note: The code above is slightly incomplete, it's just to give some context to the answer

For strings you can use something like:

const ENEMIES: &'static [&'static str] = &["monster", "ghost"];

Kaplan · Accepted Answer · 2022-01-26 17:10:09Z

1

Nowadays You can write it without indirection through a pointer:

const ONETWO: [u8;2]   = [1, 2];
const ARRAY:  [&str;2] = ["Hello", "World"];

fn main() {
    println!("{} {}", ONETWO[0], ONETWO[1]);  // 1 2
    println!("{} {}", ARRAY[0], ARRAY[1]);  // Hello World
}

Thanks to static lifetime elision, you usually don’t have to explicitly use

'static like in:

const ARRAY: [&'static str;2] = ["Hello", "World"];

edited Jan 26, 2022 at 17:10

answered Nov 20, 2021 at 9:54

Kaplan

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