wat now?

gistfile1.rs

// My objective is to return an environment variable parsed as an integer, 
// and if either the environment variable isn't set, or it can't be parsed as 
// an integer, return a default value.

// This works, but is kind of ugly ...
fn u32_from_env_with_default(env: &str, default: u32) -> u32 {
    let tmp_1 = std::env::var(env);
    if tmp_1.is_ok() {
        let tmp_2 = tmp_1.unwrap().parse::<u32>();
        if tmp_2.is_ok() {
            tmp_2.unwrap()
        } else {
            default
        }
    } else {
        default
    }
}

// While this doesn't work, ... but is there a way to do it somewhat like this?
fn u32_from_env_with_default(env: &str, default: u32) -> u32 {
    std::env::var(env).and_then(|v| v.parse::<u32>()).unwrap_or(default)
}
// src/main.rs:63:37: 63:53 error: mismatched types:
//  expected `core::result::Result<_, std::env::VarError>`,
//     found `core::result::Result<u32, core::num::ParseIntError>`
// (expected enum `std::env::VarError`,
//     found struct `core::num::ParseIntError`) [E0308]
// src/main.rs:63     std::env::var(env).and_then(|v| v.parse::<u32>()).unwrap_or(default)
//                                                    ^~~~~~~~~~~~~~~~
// error: aborting due to previous error


// This works by turning the Results into Options.
fn u32_from_env_with_default(env: &str, default: u32) -> u32 {
    std::env::var(env).ok()
        .and_then(|v| v.parse::<u32>().ok())
        .unwrap_or(default)
}