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// You can use clap's value_t! macro with a custom enum by implementing the std::str::FromStr
// trait which is very straight forward. There are three ways to do this, for simple enums
// meaning those that don't require 'pub' or any '#[derive()]' directives you can use clap's
// simple_enum! macro. For those that require 'pub' or any '#[derive()]'s you can use clap's
// arg_enum! macro. The third way is to implement std::str::FromStr manually.
// In most circumstances using either simple_enum! or arg_enum! is fine.
// In the following example we will create two enums using macros, assign a positional argument
// that accepts only one of those values, and use clap to parse the argument.
// Add clap like normal
extern crate clap;
use clap::{App, Arg};
// Using arg_enum! is more like traditional enum declarations
// **NOTE:** Only bare variants are supported
pub enum Oof {
enum Foo {
fn main() {
// Create the application like normal
let enum_vals = ["fast", "slow"];
let m = App::new("myapp")
// Use a single positional argument that is required
.arg(Arg::from_usage("<foo> 'The Foo to use'")
.arg(Arg::from_usage("<speed> 'The speed to use'")
// You can define a list of possible values if you want the values to be
// displayed in the help information. Whether you use possible_values() or
// not, the valid values will ALWAYS be displayed on a failed parse.
// For the second positional, lets not use possible_values() just to show the difference
.arg_from_usage("<oof> 'The Oof to use'")
let t = value_t!(m.value_of("foo"), Foo).unwrap_or_else(|e| e.exit());
let t2 = value_t!(m.value_of("oof"), Oof).unwrap_or_else(|e| e.exit());
// Now we can use our enum like normal.
match t {
Foo::Bar => println!("Found a Bar"),
Foo::Baz => println!("Found a Baz"),
Foo::Qux => println!("Found a Qux")
// Since our Oof derives Debug, we can do this:
println!("Oof: {:?}", t2);
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