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Update Result docs to the new guarantees #124870

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Update Result docs to the new guarantees #124870

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f94fa6b
Some Result combinations work like an Option.
Lokathor May 8, 2024
10f8d1f
use teletype on the attribute name
Lokathor May 8, 2024
b468f21
Don't use `T` with both Result and Option, improve explanation.
Lokathor May 13, 2024
939f267
revert to the inconsistent paragraph wrapping.
Lokathor May 25, 2024
22668e8
Resolve https://github.com/rust-lang/rust/pull/124870#issuecomment-21…
Lokathor May 25, 2024
2e8f14f
correct for copy paste errors when fixing wrapping.
Lokathor May 25, 2024
2b2f83e
github showed that weird.
Lokathor May 25, 2024
f8279b1
Fix URL target, it's in the module not the type.
Lokathor May 25, 2024
9b480da
It seems that anchor names are implicitly all lowercase
Lokathor May 25, 2024
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3 changes: 3 additions & 0 deletions library/core/src/option.rs
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Expand Up @@ -137,10 +137,13 @@
//!
//! [^extern_fn]: this remains true for any argument/return types and any other ABI: `extern "abi" fn` (_e.g._, `extern "system" fn`)
//!
//! Under some conditions the above types `T` are also null pointer optimized when wrapped in a [`Result`][result_repr].
//!
//! [`Box<U>`]: ../../std/boxed/struct.Box.html
//! [`num::NonZero*`]: crate::num
//! [`ptr::NonNull<U>`]: crate::ptr::NonNull
//! [function call ABI]: ../primitive.fn.html#abi-compatibility
//! [result_repr]: crate::result#representation
//!
//! This is called the "null pointer optimization" or NPO.
//!
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21 changes: 21 additions & 0 deletions library/core/src/result.rs
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Expand Up @@ -224,6 +224,27 @@
//! [`Err(E)`]: Err
//! [io::Error]: ../../std/io/struct.Error.html "io::Error"
//!
//! # Representation
//!
//! In some cases, [`Result<T, E>`] will gain the same size, alignment, and ABI
//! guarantees as [`Option<U>`] has. One of either the `T` or `E` type must be a
//! type that qualifies for the `Option` [representation guarantees][opt-rep],
//! and the *other* type must meet all of the following conditions:
//! * Is a zero-sized type with alignment 1 (a "1-ZST").
//! * Has no fields.
//! * Does not have the `#[non_exhaustive]` attribute.
//!
//! For example, `NonZeroI32` qualifies for the `Option` representation
//! guarantees, and `()` is a zero-sized type with alignment 1, no fields, and
//! it isn't `non_exhaustive`. This means that both `Result<NonZeroI32, ()>` and
//! `Result<(), NonZeroI32>` have the same size, alignment, and ABI guarantees
//! as `Option<NonZeroI32>`. The only difference is the implied semantics:
//! * `Option<NonZeroI32>` is "a non-zero i32 might be present"
//! * `Result<NonZeroI32, ()>` is "a non-zero i32 success result, if any"
//! * `Result<(), NonZeroI32>` is "a non-zero i32 error result, if any"
//!
//! [opt-rep]: ../option/index.html#representation "Option Representation"
//!
//! # Method overview
//!
//! In addition to working with pattern matching, [`Result`] provides a
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