Function activate 

pub fn activate() -> Result<RbEnv, Box<dyn Error>>

Configures Cargo linking based on the DEP_RB_* environment variables. This is needed to ensure that Cargo properly links to libruby on Windows..

// In your crate's build.rs

pub fn main() -> Result<(), Box<dyn std::error::Error>> {
    let rb_env = rb_sys_env::activate()?;

    if rb_env.ruby_major_minor() < (2, 7) {
        panic!("Your Ruby version is EOL!");
    }

    Ok(())
}

// In your crate's lib.rs
pub fn is_ruby_flonum_activated() -> bool {
    cfg!(ruby_use_flonum)
}