envparse

Quick and dirty crate for parsing values out of an environment var provided at compile time. See also: docs.

Usage

Here's an example

const MAX_LEN: usize = envparse::parse_env!("MYCRATE_MAX_THING_LEN" as usize else 64);
struct Thing {
    len: [u8; MAX_LEN],
}

You can bound by ranges too. This one will fail because the MUST_BE_USER_PROVIDED var isn't provided.

const MAX_LEN_LOG2: u32 = envparse::parse_env!("MYCRATE_MAX_LEN_LOG2" as u32 in 0..32);
const MAX_LEN: usize = 1 << MAX_LEN_LOG2;
struct Thing {
    len: [u8; MAX_LEN],
}

You can also try

const MAX_LEN_LOG2: u32 = match envparse::parse_env!(try "OPTIONAL_MAX_LEN_LOG2" as u32 in 0..32) {
    Some(v) => v,
    None => 5,
}
const MAX_LEN: usize = 1 << MAX_LEN_LOG2;
struct Thing {
    len: [u8; MAX_LEN],
}