Updated example code in the documentation

[green-coder]

An example code was truncated to only its first line. I went to find the missing part in the source code of Rust, and now the documentation makes sense.

[rust-highfive]

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[alexcrichton]

r? @steveklabnik

[steveklabnik]

The intention here was to show the type signature, not the implementation. Maybe we can fix it some other way to make it clear without showing the internals?

[green-coder]

But if you read the text right after, it looked like the reader was expected to see that the implementation was returning the iterator directly while it was not visible before the fix.

[steveklabnik]

Could we maybe instead change the above sentence to say something like "look at the type signature of this implementation"? Would that make it more clear? the body is just a distraction.

[green-coder]

The text around this modification is :

//! There's one more subtle bit here: the standard library contains an
//! interesting implementation of [`IntoIterator`]:
//!
//! ```ignore
//! impl<I: Iterator> IntoIterator for I {
//!     type Item = I::Item;
//!     type IntoIter = I;
//! 
//!     fn into_iter(self) -> I {
//!         self
//!     }
//! }
//! ```
//!
//! In other words, all [`Iterator`]s implement [`IntoIterator`], by just
//! returning themselves. This means two things:
//!
//! 1. If you're writing an [`Iterator`], you can use it with a `for` loop.
//! 2. If you're creating a collection, implementing [`IntoIterator`] for it
//!    will allow your collection to be used with the `for` loop.
//!

In my humble uninformed reader's experience (because I read it as a beginner learning Rust), it makes sense to show the implementation (the function returning self) more than to show the types above.

I suggest to simplify the example by replacing the lines:

//!     type Item = I::Item;
//!     type IntoIter = I;

by //! // [...].

[steveklabnik]

I really do not want to write out the implementation here, sorry. I know that it may aid your understanding, but I don't want to expose internals like this, as a general rule. The source is still there to look at, in the end.

Thank you for the PR, but I don't think I can accept it.