book: Clarify that trait or type must be in same crate as impl

[kamalmarhubi]

No description provided.

[kamalmarhubi]

r? @steveklabnik

[rust-highfive]

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

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[kamalmarhubi]

@bors rollup

[kamalmarhubi]

Or something :p

[kamalmarhubi]

Since the chapter on traits comes before the one on crates, would it make sense to either quick-define crates or reference the chapter?

[steveklabnik]

Yes, we need a forward reference to the crates chapter.

(and @bors will only listen to people with permission 😉 )

[kamalmarhubi]

Of course.

And done.

[steveklabnik]

@bors: r+ rollup

thank you so much!

[bors]

📌 Commit a559577 has been approved by steveklabnik