env_cast! reads an environment variable just like env!("XXX"), but parses it into a specific type.
Supported types are currently
i8, u8, i16, u16, i32, u32, i64, u64, f32, f64.
rust
use env_cast::env_cast;
let PKG_MAJOR: u32 = env_cast!("CARGO_PKG_VERSION_MAJOR" as u32);