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Rollup merge of #46548 - jonathanstrong:master, r=dtolnay

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Recommends lazily evaluated alternatives for `Option::or` and `Result::or`

Adds language to docs for `Option` and `Result` recommending the use of lazily evaluated alternatives when appropriate. These comments are intended to echo a [clippy lint] on the same topic. The [reddit discussion] may also be of interest.

[clippy lint]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#or_fun_call
[reddit discussion]: https://www.reddit.com/r/rust/comments/7hutqn/perils_of_optionor_and_resultor/
This commit is contained in:
Guillaume Gomez 2017-12-07 23:59:04 +01:00 • committed by GitHub
commit 0b47f02267
2 changed files with 27 additions and 0 deletions
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17
src/libcore/option.rs
View file

@ -338,6 +338,12 @@ impl<T> Option<T> {
/// Returns the contained value or a default.
///
/// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
/// the result of a function call, it is recommended to use [`unwrap_or_else`],
/// which is lazily evaluated.
///
/// [`unwrap_or_else`]: #method.unwrap_or_else
///
/// # Examples
///
/// ```
@ -451,11 +457,16 @@ impl<T> Option<T> {
/// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to
/// [`Ok(v)`] and [`None`] to [`Err(err)`].
///
/// Arguments passed to `ok_or` are eagerly evaluated; if you are passing the
/// result of a function call, it is recommended to use [`ok_or_else`], which is
/// lazily evaluated.
///
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
/// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok
/// [`Err(err)`]: ../../std/result/enum.Result.html#variant.Err
/// [`None`]: #variant.None
/// [`Some(v)`]: #variant.Some
/// [`ok_or_else`]: #method.ok_or_else
///
/// # Examples
///
@ -644,6 +655,12 @@ impl<T> Option<T> {
/// Returns the option if it contains a value, otherwise returns `optb`.
///
/// Arguments passed to `or` are eagerly evaluated; if you are passing the
/// result of a function call, it is recommended to use [`or_else`], which is
/// lazily evaluated.
///
/// [`or_else`]: #method.or_else
///
/// # Examples
///
/// ```

10
src/libcore/result.rs
View file

@ -625,8 +625,13 @@ impl<T, E> Result<T, E> {
/// Returns `res` if the result is [`Err`], otherwise returns the [`Ok`] value of `self`.
///
/// Arguments passed to `or` are eagerly evaluated; if you are passing the
/// result of a function call, it is recommended to use [`or_else`], which is
/// lazily evaluated.
///
/// [`Ok`]: enum.Result.html#variant.Ok
/// [`Err`]: enum.Result.html#variant.Err
/// [`or_else`]: #method.or_else
///
/// # Examples
///
@ -690,8 +695,13 @@ impl<T, E> Result<T, E> {
/// Unwraps a result, yielding the content of an [`Ok`].
/// Else, it returns `optb`.
///
/// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
/// the result of a function call, it is recommended to use [`unwrap_or_else`],
/// which is lazily evaluated.
///
/// [`Ok`]: enum.Result.html#variant.Ok
/// [`Err`]: enum.Result.html#variant.Err
/// [`unwrap_or_else`]: #method.unwrap_or_else
///
/// # Examples
///