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Rollup merge of rust-lang#95787 - yaahc:panic-doc-update-v2, r=dtolnay
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reword panic vs result section to remove recoverable vs unrecoverable framing

Based on feedback from the Error Handling FAQ: rust-lang/project-error-handling#50 (comment)

r? ````@dtolnay````
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Dylan-DPC authored Apr 9, 2022
2 parents 0051301 + aa3c141 commit 8d73922
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34 changes: 22 additions & 12 deletions library/core/src/macros/panic.md
Original file line number Diff line number Diff line change
Expand Up @@ -24,20 +24,30 @@ See also the macro [`compile_error!`], for raising errors during compilation.

# When to use `panic!` vs `Result`

The Rust model of error handling groups errors into two major categories:
recoverable and unrecoverable errors. For a recoverable error, such as a file
not found error, it’s reasonable to report the problem to the user and retry
the operation. Unrecoverable errors are always symptoms of bugs, like trying to
access a location beyond the end of an array.
The Rust language provides two complementary systems for constructing /
representing, reporting, propagating, reacting to, and discarding errors. These
responsibilities are collectively known as "error handling." `panic!` and
`Result` are similar in that they are each the primary interface of their
respective error handling systems; however, the meaning these interfaces attach
to their errors and the responsibilities they fulfill within their respective
error handling systems differ.

The Rust language and standard library provides `Result` and `panic!` as parts
of two complementary systems for representing, reporting, propagating, reacting
to, and discarding errors for in these two categories.
The `panic!` macro is used to construct errors that represent a bug that has
been detected in your program. With `panic!` you provide a message that
describes the bug and the language then constructs an error with that message,
reports it, and propagates it for you.

The `panic!` macro is provided to represent unrecoverable errors, whereas the
`Result` enum is provided to represent recoverable errors. For more detailed
information about error handling check out the [book] or the [`std::result`]
module docs.
`Result` on the other hand is used to wrap other types that represent either
the successful result of some computation, `Ok(T)`, or error types that
represent an anticipated runtime failure mode of that computation, `Err(E)`.
`Result` is used alongside user defined types which represent the various
anticipated runtime failure modes that the associated computation could
encounter. `Result` must be propagated manually, often with the the help of the
`?` operator and `Try` trait, and they must be reported manually, often with
the help of the `Error` trait.

For more detailed information about error handling check out the [book] or the
[`std::result`] module docs.

[ounwrap]: Option::unwrap
[runwrap]: Result::unwrap
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