README.md

envparse

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

Feel free to email me if I fail to notice a PR or issue in this repository (my github notifications are a mess).

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 to parse the value, which always returns an Option. Note that if the user provided the value, but it was out of range, this will still fail with a compile error (rather than returning None), in order to let them know that their configuration was not/cannot be respected.

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],
}