# How to do "do" blocks

**URL:** <https://www.ruby-forum.com/t/how-to-do-do-blocks/115762>\
**Category:** Ruby\
**Created:** [September 28, 2007, 10:13am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762 "2007-09-28T10:13:16Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 10:13am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/1 "2007-09-28T10:13:16Z")

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How come this works:

collection\_of\_objects = []  
10.times do  
collection\_of\_objects \<\< MyObject.create  
end

But this doesn’t:

collection\_of\_objects = []  
10.times do { collection\_of\_objects \<\< MyObject.create }

I didn’t understand there was ANY difference between the two syntaxes  
really. Can someone explain to me the finer points?

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**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 10:23am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/2 "2007-09-28T10:23:28Z")

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Take the “do” out of the statement when passing a block in {}:

collection\_of\_objects = []  
10.times {collection\_of\_objects \<\< MyObject.create}

🙂

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 10:20am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/3 "2007-09-28T10:20:32Z")

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On 9/28/07, Daniel T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> 10.times do { collection\_of\_objects \<\< MyObject.create }
> 
> I didn’t understand there was ANY difference between the two syntaxes  
> really. Can someone explain to me the finer points?

The reason is that “do” starts a block, and then inside the block the  
{} are parsed as a hash literal:

irb(main):001:0\> collection\_of\_objects = []  
=\> []  
irb(main):002:0\> 10.times do { collection\_of\_objects \<\< MyObject.create  
}  
irb(main):003:1\> end  
SyntaxError: compile error  
(irb):2: odd number list for Hash  
from (irb):3  
from :0

You have to use only one form of block, either do…end or {}. The  
convention seems to be to use do…end for multiline blocks, while {}  
is used for one-liners.

irb(main):005:0\> 10.times { collection\_of\_objects \<\< Array.new }  
=\> 10  
irb(main):006:0\> collection\_of\_objects  
=\> [[], [], [], [], [], [], [], [], [], []]

Regards,

Jesus.

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 11:00am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/4 "2007-09-28T11:00:23Z")

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On 9/28/07, Daniel T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> [http://onestepback.org/index.cgi/Tech/Ruby/BraceVsDoEnd.rdoc](http://onestepback.org/index.cgi/Tech/Ruby/BraceVsDoEnd.rdoc)
> 
> In the first post, one of the commenters asks:
> 
> > As for using {} only when returning a value, doesn’t every statement return a  
> > value (in your example, the array with it’s elements capitalised and reversed)?
> 
> And although he’s wrong, the code in question:  
> i.capitalize!  
> is in-place changing the variable of course… but his point is still  
> valid. Anyone want to weigh in on this?

I’m fairly new to Ruby, and still trying to accomodate my style  
(coming from java it’s taking me a while to use do…end, my fingers  
type the { automatically :-), but I’m pretty sure I’ve read many times  
here what I said above, and those articles also imply that’s the more  
widely accepted answer to that question.

I can’t comment on other people’s uses of this. Maybe more  
knowledgeable people here could chime in?

Jesus.

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 10:39am UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/5 "2007-09-28T10:39:16Z")

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Well thanks fellas… that makes good sense.

> You have to use only one form of block, either do…end or {}. The  
> convention seems to be to use do…end for multiline blocks, while {}  
> is used for one-liners.

However, there’s some lines of thought on the internet that have a  
different idea. What do you think of the idea that it’s not “one line  
vs. multiline” but “returns a value vs. doesn’t return a value”.

Here’s the two posts I’m talking about:  
[http://objo.com/2007/6/28/ruby-style-ruby-do-end-versus](http://objo.com/2007/6/28/ruby-style-ruby-do-end-versus)  
[http://onestepback.org/index.cgi/Tech/Ruby/BraceVsDoEnd.rdoc](http://onestepback.org/index.cgi/Tech/Ruby/BraceVsDoEnd.rdoc)

In the first post, one of the commenters asks:

> As for using {} only when returning a value, doesn’t every statement return a  
> value (in your example, the array with it’s elements capitalised and reversed)?

And although he’s wrong, the code in question:  
i.capitalize!  
is in-place changing the variable of course… but his point is still  
valid. Anyone want to weigh in on this?

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 6:35pm UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/6 "2007-09-28T18:35:12Z")

</div>

> However, there’s some lines of thought on the internet that have a  
> different idea. What do you think of the idea that it’s not “one line  
> vs. multiline” but “returns a value vs. doesn’t return a value”.

All Ruby blocks (and methods) return a value. They return the value  
of the last statement in the block.  
But only if you explicitly use it.  
Assign it to something, or use return if you want it to be obvious.

The convention is simply  
{} for one-line  
do-end for multi-line

You don’t have to follow these rules. It is up to you.

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [October 2, 2007, 5:10pm UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/7 "2007-10-02T17:10:22Z")

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On 9/28/07, Daniel T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Here’s the two posts I’m talking about:  
> valid. Anyone want to weigh in on this?  
> [http://talklikeaduck.denhaven2.com/articles/2007/10/02/ruby-blocks-do-or-brace](http://talklikeaduck.denhaven2.com/articles/2007/10/02/ruby-blocks-do-or-brace)

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [October 3, 2007, 1:55pm UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/8 "2007-10-03T13:55:55Z")

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Hi –

On Fri, 28 Sep 2007, Bertram S. wrote:

> > >
> 
> ```
> puts "((("
> 
> ```
> 
> (((
> 
> Not a very intuitive example I admit.

Here’s one I’ve stumbled on in real life:

irb(main):001:0\> a = [1,2,3,4]  
=\> [1, 2, 3, 4]  
irb(main):002:0\> puts a.map {|e| e \* 10 }  
10  
20  
30  
40  
=\> nil  
irb(main):003:0\> puts a.map do |e| e \* 10 end  
1  
2  
3  
4  
=\> nil

David

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<div class="post-metadata">

**Author:** ![datorrey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cab0a1/32.png) [@datorrey](https://www.ruby-forum.com/u/datorrey)\
**Post date:** [September 28, 2007, 12:03pm UTC](https://www.ruby-forum.com/t/how-to-do-do-blocks/115762/9 "2007-09-28T12:03:37Z")

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Hi,

Am Freitag, 28. Sep 2007, 17:20:40 +0900 schrieb Tom M.:

> Take the “do” out of the statement when passing a block in {}:
> 
> 10.times {collection\_of\_objects \<\< MyObject.create}

Yet another opportunity to mention that {} has higer  
precedence than do…end.

```
def f
  puts "((("
  yield if block_given?
  puts ")))"
end
def g x
  puts "[[[#{x}|"
  yield if block_given?
  puts "]]]"
end

```

> g f { puts “x” }  
> (((  
> x  
> )))  
> [[[|  
> ]]]  
> g f do puts “x” end  
> (((  
> )))  
> [[[|  
> x  
> ]]]

Not a very intuitive example I admit.

Bertram