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Document that Display entails ToString and should be lossless and infallible #94488

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Document that Display entails ToString and should be lossless and infallible #94488

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Document that Display entails ToString and should be lossless and inf…
Mar 1, 2022
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Merge branch 'rust-lang:master' into issue-92941-fix
JKAnderson409 Jun 18, 2022
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14 changes: 12 additions & 2 deletions library/core/src/fmt/mod.rs
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Expand Up @@ -703,11 +703,21 @@ pub use macros::Debug;

/// Format trait for an empty format, `{}`.
///
/// `Display` is similar to [`Debug`], but `Display` is for user-facing
/// output, and so cannot be derived.
/// `Display` is similar to [`Debug`], but `Display` is for user-facing output,
/// and so cannot be derived. When `Display` is implemented, the [`ToString`]
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/// `Display` is similar to [`Debug`], but `Display` is for user-facing output,
/// and so cannot be derived. When `Display` is implemented, the [`ToString`]
/// `Display` is similar to [`Debug`], but `Display` is for user-facing output.
/// When `Display` is implemented, the [`ToString`]

As long as we're fixing this documentation: this conclusion doesn't actually automatically follow, and might not always be true.

/// trait is implemented automatically, adding the `to_string` method to all
/// `Display` types.
///
/// A `Display` implementation should be lossless and infallible, otherwise it
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How do you define lossless here? Any definition I can think of feels way too strict..

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"doesn't lose information from its internal data" and then we can use Path as an example?

/// does not fit the API. For example, converting a path to a [`String`] is
/// potentially lossy or fallible, so [`Path`] doesn’t implement `Display`
/// directly (but offers a .display() method).
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/// directly (but offers a .display() method).
/// directly (but offers a `.display()` method).

///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [`Path`]: ../../std/path/struct.Path.html
/// [`ToString`]: ../../std/string/trait.ToString.html
/// [`String`]: ../../std/string/struct.String.html
/// [module]: ../../std/fmt/index.html
///
/// # Examples
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