ref-cast 1.0.6

Safely cast &T to &U where the struct U contains a single field of type T.
Documentation 
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use std::env;
use std::process::Command;
use std::str;

fn main() {
    if let Some(rustc) = rustc_minor_version() {
        if rustc < 38 {
            println!("cargo:rustc-cfg=no_intrinsic_type_name");
        }
    }
}

fn rustc_minor_version() -> Option<u32> {
    let rustc = env::var_os("RUSTC")?;
    let output = Command::new(rustc).arg("--version").output().ok()?;
    let version = str::from_utf8(&output.stdout).ok()?;
    let mut pieces = version.split('.');
    if pieces.next() != Some("rustc 1") {
        return None;
    }
    pieces.next()?.parse().ok()
}