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comp.lang.ruby

Hash questions

Hunt Jon

4/9/2009 2:18:00 PM

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
6 Answers

Todd Benson

4/9/2009 2:29:00 PM

0

On Thu, Apr 9, 2009 at 9:18 AM, Hunt Jon <jona.hunt777@gmail.com> 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

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

Adam Gardner

4/9/2009 2:33:00 PM

0

Hunt Jon 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.
--
Posted via http://www.ruby-....

Adam Gardner

4/9/2009 2:36:00 PM

0


> 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 {.
--
Posted via http://www.ruby-....

Rick DeNatale

4/9/2009 2:45:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

On Thu, Apr 9, 2009 at 10:35 AM, Adam Gardner <adam.oddfellow@gmail.com>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.
> >
> > 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 {.
>

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.denh...
Twitter: http://twitter.com/Ri...
WWR: http://www.workingwithrails.com/person/9021-ric...
LinkedIn: http://www.linkedin.com/in/ri...

Robert Klemme

4/9/2009 2:47:00 PM

0

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 Gardner <adam.oddfellow@gmail.com>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

Phlip

4/9/2009 2:53:00 PM

0

Robert Klemme 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".