Is there a way to print enum values?

Question

Is there an easy way to format and print enum values? I expected that they'd have a default implementation of std::fmt::Display, but that doesn't appear to be the case.

enum Suit {     Heart,     Diamond,     Spade,     Club }  fn main() {     let s: Suit = Suit::Heart;     println!("{}", s); } 

Desired output: Heart

Error:

error[E0277]: the trait bound `Suit: std::fmt::Display` is not satisfied   --> src/main.rs:10:20    | 10 |     println!("{}", s);    |                    ^ the trait `std::fmt::Display` is not implemented for `Suit`    |    = note: `Suit` cannot be formatted with the default formatter; try using `:?` instead if you are using a format string    = note: required by `std::fmt::Display::fmt` 

Answer 1

You can derive an implementation of std::format::Debug:

#[derive(Debug)] enum Suit {     Heart,     Diamond,     Spade,     Club }  fn main() {     let s = Suit::Heart;     println!("{:?}", s); } 

It is not possible to derive Display because Display is aimed at displaying to humans and the compiler cannot automatically decide what is an appropriate style for that case. Debug is intended for programmers, so an internals-exposing view can be automatically generated.

Answer 2

The Debug trait prints out the name of the Enumvariant.

If you need to format the output, you can implement Display for your Enum like so:

use std::fmt;  enum Suit {     Heart,     Diamond,     Spade,     Club }  impl fmt::Display for Suit {     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {        match *self {            Suit::Heart => write!(f, "♥"),            Suit::Diamond => write!(f, "♦"),            Suit::Spade => write!(f, "♠"),            Suit::Club => write!(f, "♣"),        }     } }  fn main() {     let heart = Suit::Heart;     println!("{}", heart); }