[dozzie]

Certainly functional programming is not making the data containers to fulfil a separately defined interface. This comes from OOP paradigm (its form that is implemented in most languages).

And then, what specifically does "functional programming" mean to you that makes implementing an interface a feature from functional paradigm?

But this all misses the point of my comment. If you knew it would invoke the unnecessary discussion to call the iterator "functional feature" (as the quoted comment signifies), you should have rephrased the title of the chapter in the first place, rendering the disclaimer unnecessary.

[steveklabnik]

You didn't answer my question.

[dozzie]

I did, at least the relevant parts of your question. And it still stands that you missed my point that you just created a contention point fully knowing that it is useless contention (your quoted remark from the chapter prooves both that you knew it will be problematic and that you didn't need it there).

[sixbrx]

No OO style interfaces here, Ierator and IntoIterator are traits, which are more akin to a type class from Haskell than an interface as seen in OO languages