# Hash questions

**URL:** <https://www.ruby-forum.com/t/hash-questions/165149>\
**Category:** Ruby\
**Created:** [April 9, 2009, 4:18pm UTC](https://www.ruby-forum.com/t/hash-questions/165149 "2009-04-09T16:18:47Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:18pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/1 "2009-04-09T16:18:47Z")

</div>

When I run:

p {“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }

I get an error.

But when I run:

x = {“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }  
p x

There’s no error.

What’s the difference between the two?

John

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:29pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/2 "2009-04-09T16:29:57Z")

</div>

On Thu, Apr 9, 2009 at 9:18 AM, Hunt J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> There’s no error.
> 
> What’s the difference between the two?
> 
> John

p( {“foo” =\> 1, “bar” =\> 2, “baz” =\> 3} )

You need parentheses in the first case, I believe, so the that the  
parser knows you are not trying to send a block to the method #p.

Todd

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:33pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/3 "2009-04-09T16:33:15Z")

</div>

Hunt J. wrote:

> When I run:
> 
> p {“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }
> 
> I get an error.
> 
> But when I run:
> 
> x = {“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }  
> p x
> 
> There’s no error.
> 
> What’s the difference between the two?
> 
> John

From what I can tell, ruby is interpreting the beginning of your hash as  
the beginning of a block, instead;  
p({“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }) works as intended.

This is seems like a bug to me, although whether it’s a bug with the  
parser (finding a block where it should be looking for a hash literal),  
a bug with p (asking for a block when it doesn’t use one) or the  
documentation (failing to mention that p accepts a block), I’m not sure.

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:45pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/4 "2009-04-09T16:45:48Z")

</div>

On Thu, Apr 9, 2009 at 10:35 AM, Adam G.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> Actually, on a bit more inspection, both puts and print work the same  
> way, and I imagine there are other methods that do this as well. This  
> just seems like the parser failing to correctly interpret the ambiguity  
> of a {.

No, I’d say that the parser is correctly parsing an initial ‘{’ after a  
method invocation as a block argument to the invocation.

There’s no need to mention that p, or any other method can be given a  
block  
since ANY ruby method can be given (and by default) ignore a block.  
It’s  
just part of the language that you need to learn, like the need to use  
self.x = value to invoke an attribute writer method to disambiguate  
between  
x= as a method and x as a local variable.

–  
Rick DeNatale

Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)  
Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale)  
WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale)  
LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:51pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/5 "2009-04-09T16:51:04Z")

</div>

On 09.04.2009 16:44, Rick DeNatale wrote:

> [Note: parts of this message were removed to make it a legal post.]
> 
> On Thu, Apr 9, 2009 at 10:35 AM, Adam G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:
> 
> > > From what I can tell, ruby is interpreting the beginning of your hash as  
> > > the beginning of a block, instead;  
> > > p({“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }) works as intended.

Here’s an alternative

p( “foo” =\> 1, “bar” =\> 2, “baz” =\> 3 )

And no, the observed behavior is not a bug as Rick pointed out.

Cheers

robert

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:35pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/6 "2009-04-09T16:35:18Z")

</div>

> From what I can tell, ruby is interpreting the beginning of your hash as  
> the beginning of a block, instead;  
> p({“foo” =\> 1, “bar” =\> 2, “baz” =\> 3 }) works as intended.
> 
> This is seems like a bug to me, although whether it’s a bug with the  
> parser (finding a block where it should be looking for a hash literal),  
> a bug with p (asking for a block when it doesn’t use one) or the  
> documentation (failing to mention that p accepts a block), I’m not sure.

Actually, on a bit more inspection, both puts and print work the same  
way, and I imagine there are other methods that do this as well. This  
just seems like the parser failing to correctly interpret the ambiguity  
of a {.

---

<div class="post-metadata">

**Author:** ![Hunt\_J](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/b9e5f3/32.png) [@Hunt\_J](https://www.ruby-forum.com/u/Hunt_J)\
**Post date:** [April 9, 2009, 4:58pm UTC](https://www.ruby-forum.com/t/hash-questions/165149/7 "2009-04-09T16:58:42Z")

</div>

Robert K. wrote:

> p( “foo” =\> 1, “bar” =\> 2, “baz” =\> 3 )
> 
> And no, the observed behavior is not a bug as Rick pointed out.

The freedom to skip () parens nearly everywhere comes at a price. You  
gotta  
think of the space following a method name as a tiny little operator  
meaning  
“introduce arguments here like a ( would have”.