// In the following example we will create an enum with 4 values, assign a positional argument // that accepts only one of those values, and use clap to parse the argument. // // Start with bringing the trait into scope. use std::str::FromStr; // Add clap like normal use clap::{App, Arg}; // Define your enum enum Vals { Foo, Bar, Baz, Qux, } // Implement the trait impl FromStr for Vals { type Err = &'static str; fn from_str(s: &str) -> Result { match s { "Foo" => Ok(Vals::Foo), "Bar" => Ok(Vals::Bar), "Baz" => Ok(Vals::Baz), "Qux" => Ok(Vals::Qux), _ => Err("no match"), } } } fn main() { // Create the application like normal let m = App::new("myapp") // Use a single positional argument that is required .arg( Arg::from(" 'The type to use'") // Define the list of possible values .possible_values(["Foo", "Bar", "Baz", "Qux"]), ) .get_matches(); // Note that you don't have to specify the type since rustc can infer it for you let t = m.value_of_t("type").unwrap_or_else(|e| e.exit()); // Now we can use our enum like normal. match t { Vals::Foo => println!("Found a Foo"), Vals::Bar => println!("Found a Bar"), Vals::Baz => println!("Found a Baz"), Vals::Qux => println!("Found a Qux"), } }