Rust: Option<T> should impl Display

[Boscop]

Option<T> should impl Display so that it renders as "Some(x)" where x is using T's Display impl.

[sfackler]

Why?

[Mark-Simulacrum]

I disagree; Some doesn't seem like something we should assume the user wants to expose to the "public." Arguably this isn't really something that the standard library should support, though a crate could easily do so.

[jonas-schievink]

Some(x) doesn't really look suitable for end-user consumption

[Boscop]

@Mark-Simulacrum But another crate can't do it because of orphan rules:
https://play.rust-lang.org/?gist=8785d227d9fab78aa38e336eee721b88&version=nightly

[zackmdavis]

@Boscop You may want the Debug trait (which is implemented for Option<T> when T is Debug)? The Debug formatting syntax is just two extra characters:

fn main() {
    println!("{:?}", Some(42)); // prints `Some(42)`
}

[Mark-Simulacrum]

@Boscop It'd be a newtype like this https://play.rust-lang.org/?gist=3d3e1bfcaba776ba623b8faae3d9036d&version=nightly.

[scottmcm]

Previous discussion: https://internals.rust-lang.org/t/impl-t-display-display-for-option-t/6051

[Cobrand]

Like @zackmdavis said, I think you're better off with the Debug trait. Take for instance a Option<&str>, here is how few of those would display:

• Some("Option") -> "Some(Option)"
• Some("") -> "Some()"
• Some("UdpSocket") -> "Some(UdpSocket)"

This doesn't seem very intuitive to me.

Something "plausible" would be to impl Display for Option<&str> and the likes, where Some("some string") would display as some string and None would be displayed as nothing (0 characters). But in anycase, I think this is too specific to be in the standard library.

[Boscop]

@zackmdavis @Cobrand I'm aware of that but I need to render using the Display impl of T, not its Debug impl..
@Mark-Simulacrum Thanks, I guess I will use that for now..

[kdy1]

I think only way to provide valid implementation for any type is using a trait like OptionDisplay and implement Display for Option where T: OptionDisplay.

Although almost all types in std cannot implement it, it would be quite useful for newtype structs.