Fix "Display type" to "Display trait" in ch19-03

[generalmimon]

Display is a trait, not a type. See https://doc.rust-lang.org/std/fmt/trait.Display.html:

Trait std::fmt::Display

pub trait Display {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}

[chriskrycho]

Traits are types, so the text is accurate here! While it is sometimes important to distinguish between traits and other types, in this case the text seems perfectly fine as is, so I am going to close this. 😅 Thanks, though!

[generalmimon]

@chriskrycho:

Traits are types, so the text is accurate here!

Really? Pretty much every answer by different people for example in this thread at Reddit says otherwise:

https://www.reddit.com/r/rust/comments/130cxak/comment/jhwadxr/

Firstly, traits are not types - you can't create instance of a trait. The purpose of traits is to define some functionality that types may share.

https://www.reddit.com/r/rust/comments/130cxak/comment/jhw8ewi/

Traits are not types in Rust. There are two ways you can use them in a type position: (...)

https://www.reddit.com/r/rust/comments/130cxak/comment/jhwotrm/

Traits aren't types. They can pretty much only be used to either organize your code better, or more importantly, tell Rust what kind of methods you can call on an "unknown" type.

https://www.reddit.com/r/rust/comments/130cxak/comment/ji8ha4t/

You can't use a trait as a type. It's way closer to a limited interface; a "contract" that dictates that everyone that implements it must implement one or more functions as well.

---

Are all these people wrong? And even if they are, it is still better to insist on keeping "Display type" in the text (when really the "Display trait" was intended) when it's clearly not aligned with what many people believe?

Also, for the sake of interest, this is the only occurrence of "Display type" in the entire book (see NOT path:nostarch "`Display` type"), whereas "Display trait" comes up 10 times (see NOT path:nostarch "`Display` trait"), out of which 4 times in the same chapter ch19-03 as this unique "Display type". Just saying...

[chriskrycho]

Interesting! I'll reevaluate and chat with @carols10cents – thanks.

[carols10cents]

On further review, let's merge this. Thank you for your patience @generalmimon