Document eager evaluation of bool::then_some argument

[Adam-Gleave]

I encountered this earlier today and thought maybe bool::then_some could use a little addition to the documentation.

It's pretty obvious with familiarity and from looking at the implementation, but the argument for then_some is eagerly evaluated, which means if you do the following (as I did), you can have a problem:

// Oops!
let _ = something
    .has_another_thing()
    .then_some(something.another_thing_or_panic());

A note, similar to other methods with eagerly-evaluated arguments and a lazy alternative (Option::or, for example), could help point this out to people who forget (like me)!

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @scottmcm (or someone else) soon.

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[scottmcm]

This looks like essentially the same phrasing as is used on https://doc.rust-lang.org/std/option/enum.Option.html#method.map_or, so it makes sense to me. Thanks!

@bors r+ rollup

@Adam-Gleave Consider also suggesting a clippy lint for this, like there is for https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call

[bors]

📌 Commit 33afe97 has been approved by scottmcm

It is now in the queue for this repository.

[Adam-Gleave]

This looks like essentially the same phrasing as is used on https://doc.rust-lang.org/std/option/enum.Option.html#method.map_or, so it makes sense to me. Thanks!

@bors r+ rollup

@Adam-Gleave Consider also suggesting a clippy lint for this, like there is for https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call

Brilliant, thanks!

Good idea, a clippy lint would be nice to have.