rust-lang · bors · Oct 6, 2023 · Sep 30, 2023 · Oct 4, 2023 · Oct 5, 2023
diff --git a/library/core/src/convert/mod.rs b/library/core/src/convert/mod.rs
@@ -479,6 479,46 @@ pub trait Into<T>: Sized {
 /// - `From<T> for U` implies [`Into`]`<U> for T`
 /// - `From` is reflexive, which means that `From<T> for T` is implemented
 ///
 /// # When to implement `From`
 ///
 /// While there's no technical restrictions on which conversions can be done using
 /// a `From` implementation, the general expectation is that the conversions
 /// should typically be restricted as follows:
 ///
 /// * The conversion is *infallible*: if the conversion can fail, use [`TryFrom`]
 /// instead; don't provide a `From` impl that panics.
 ///
 /// * The conversion is *lossless*: semantically, it should not lose or discard
 /// information. For example, `i32: From<u16>` exists, where the original
 /// value can be recovered using `u16: TryFrom<i32>`. And `String: From<&str>`
 /// exists, where you can get something equivalent to the original value via
 /// `Deref`. But `From` cannot be used to convert from `u32` to `u16`, since
 /// that cannot succeed in a lossless way. (There's some wiggle room here for
 /// information not considered semantically relevant. For example,
 /// `Box<[T]>: From<Vec<T>>` exists even though it might not preserve capacity,
 /// like how two vectors can be equal despite differing capacities.)
 ///
 /// * The conversion is *value-preserving*: the conceptual kind and meaning of
 /// the resulting value is the same, even though the Rust type and technical
 /// representation might be different. For example `-1_i8 as u8` is *lossless*,
 /// since `as` casting back can recover the original value, but that conversion
 /// is *not* available via `From` because `-1` and `255` are different conceptual
 /// values (despite being identical bit patterns technically). But
 /// `f32: From<i16>` *is* available because `1_i16` and `1.0_f32` are conceptually
 /// the same real number (despite having very different bit patterns technically).
 /// `String: From<char>` is available because they're both *text*, but
 /// `String: From<u32>` is *not* available, since `1` (a number) and `"1"`
 /// (text) are too different. (Converting values to text is instead covered
 /// by the [`Display`](crate::fmt::Display) trait.)
 ///
 /// * The conversion is *obvious*: it's the only reasonable conversion between
 /// the two types. Otherwise it's better to have it be a named method or
 /// constructor, like how [`str::as_bytes`] is a method and how integers have
 /// methods like [`u32::from_ne_bytes`], [`u32::from_le_bytes`], and
 /// [`u32::from_be_bytes`], none of which are `From` implementations. Whereas
 /// there's only one reasonable way to wrap an [`Ipv6Addr`](crate::net::Ipv6Addr)
 /// into an [`IpAddr`](crate::net::IpAddr), thus `IpAddr: From<Ipv6Addr>` exists.
 ///
 /// # Examples
 ///
 /// [`String`] implements `From<&str>`: