# Chapter 9 comment - page 188

**URL:** <https://forums.kodeco.com/t/chapter-9-comment-page-188/90489>\
**Category:** RxSwift\
**Created:** [December 5, 2019, 3:24pm UTC](https://forums.kodeco.com/t/chapter-9-comment-page-188/90489 "2019-12-05T15:24:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![konic](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/konic/32/81494_2.png) [@konic](https://forums.kodeco.com/u/konic)\
**Post date:** [December 5, 2019, 3:24pm UTC](https://forums.kodeco.com/t/chapter-9-comment-page-188/90489/1 "2019-12-05T15:24:32Z")

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The following line is not **entirely** correct:

> The Observable.concat(\_ : ) static method takes an ordered collection of observables (i.e. **an array** ).

This is related to the code:

> let observable = Observable.concat([first, second])

It works OK **without** brackets, i.e.:

> let observable = Observable.concat(first, second)

Even more, this one works OK too:

> let first = Observable.of(1, 2, 3)  
> let second = Observable.of(4, 5, 6)  
> let three = Observable.of(77)  
> let observable = Observable.concat(first, second, three)

So, I guess, words **i.e. an array** in that line is kind of misleading.

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**Author:** ![shogunkaramazov](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/shogunkaramazov/32/108826_2.png) [@shogunkaramazov](https://forums.kodeco.com/u/shogunkaramazov)\
**Post date:** [January 13, 2020, 5:02am UTC](https://forums.kodeco.com/t/chapter-9-comment-page-188/90489/2 "2020-01-13T05:02:30Z")

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@fpillet Can you please help with this when you get a chance? Thank you - much appreciated! :]

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<div class="post-metadata">

**Author:** ![fpillet](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/fpillet/32/97677_2.png) [@fpillet](https://forums.kodeco.com/u/fpillet)\
**Post date:** [January 13, 2020, 10:27am UTC](https://forums.kodeco.com/t/chapter-9-comment-page-188/90489/3 "2020-01-13T10:27:52Z")

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@konic you’re right, it’s one of the variants of the `concat` operator which takes a variable number of arguments instead of a collection (in the end result is the same but the way you pass the parameters is slightly different).

Good catch, I’ll add a note about this in the next edition!

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<div class="post-metadata">

**Author:** ![system](https://s3.amazonaws.com/cdn.raywenderlich.com/community/forum-assets/noun-game-ghost-878668.png) [@system](https://forums.kodeco.com/u/system)\
**Post date:** [May 20, 2020, 7:24am UTC](https://forums.kodeco.com/t/chapter-9-comment-page-188/90489/4 "2020-05-20T07:24:36Z")

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