# Nil? with block

**URL:** <https://www.ruby-forum.com/t/nil-with-block/89595>\
**Category:** Ruby\
**Created:** [March 21, 2007, 1:56pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595 "2007-03-21T13:56:20Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 1:56pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/1 "2007-03-21T13:56:20Z")

</div>

If you have a long chain of method calls, but want to check some  
temporary values for nils, for instance to raise an exception,  
currently the easiest way is with local variables:

e.g.:

def zipcode\_for\_user(user)  
address = user.personal\_data.address  
raise ‘no address!’ unless address  
address.zipcode  
end

If “nil?” is extended to accept a block, and to return self (for  
Object) and the result of the yield (for NilClass), the following  
notation becomes possible:

user.personal\_data.address.nil?{ raise ‘no address!’}.zipcode

This is more concise, and (I think) also more readable. The flow of  
the program isn’t broken by the nil-check. Apart from raise  
statements, it would make sense to use return statements in the  
blocks.

The implementation is trivial:  
class Object ; def nil? ; block\_given? ? self : false ; end ; end  
class NilClass ; def nil? ; block\_given? ? yield : true ; end ; end

Do you think this is a good idea?

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<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 2:05pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/2 "2007-03-21T14:05:21Z")

</div>

Hi –

On 3/21/07, Michiel de Mare [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> end  
> blocks.
> 
> The implementation is trivial:  
> class Object ; def nil? ; block\_given? ? self : false ; end ; end  
> class NilClass ; def nil? ; block\_given? ? yield : true ; end ; end
> 
> Do you think this is a good idea?

No, I don’t like it. It’s unidiomatic for a ?-method to take a block,  
and also for a block to serve as a conditional branch. I’d rather see  
it unrolled. I understand the reasoning behind it, but it ends up  
being idiosyncratic in its semantics.

David

---

<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 2:06pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/3 "2007-03-21T14:06:22Z")

</div>

On 21.03.2007 13:51, Michiel de Mare wrote:

> end
> 
> If “nil?” is extended to accept a block, and to return self (for  
> Object) and the result of the yield (for NilClass), the following  
> notation becomes possible:
> 
> user.personal\_data.address.nil?{ raise ‘no address!’}.zipcode
> 
> This is more concise, and (I think) also more readable.

Actually I am not sure about readability. Lines tend to grow pretty  
long that way. I would probably not use it. Also keep in mind that you  
will usually get an exception anyway since you’re most likely calling a  
method that nil does not support.

> The flow of  
> the program isn’t broken by the nil-check. Apart from raise  
> statements, it would make sense to use return statements in the  
> blocks.
> 
> The implementation is trivial:

… and probably slower than the current implementation as they add  
another boolean check.

> class Object ; def nil? ; block\_given? ? self : false ; end ; end  
> class NilClass ; def nil? ; block\_given? ? yield : true ; end ; end
> 
> Do you think this is a good idea?

I am not so sure. But you can easily implement this with another method  
name so you don’t have to change existing code’s behavior. Also, nil  
values might be just only one reason to throw an exception so I am not  
sure about general usefulness.

Yeah, I know - I’m a conservative skeptic. 🙂

Kind regards

robert

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<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 2:19pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/4 "2007-03-21T14:19:25Z")

</div>

> I am not so sure. But you can easily implement this with another method  
> name so you don’t have to change existing code’s behavior. Also, nil  
> values might be just only one reason to throw an exception so I am not  
> sure about general usefulness.

I also doubt this would ever be useful. I like ‘long lines’ and hate  
loads of ‘if-statements’ but I must admit I find them useful (or at  
least, any other solution looks awful to me).

Why not using, let’s call them “accessors?” which are “accessors with  
a question mark”.  
Just by hacking with a bit of “method\_missing” in both your class and  
NilClass, this would not slow exec time much I guess, and the  
implementation should also be trivial.

- in the class, you just send(accessor\_name) when you get an unknown  
accessor\_name?
- in nilclass, you return “stuff” when having a ‘?’ method (except  
nil? or empty?)

The problem, IMHO, resides in the impossibility to return a coherent  
“stuff”.  
You _want_ Ruby to NoMethodError you when you fail something.  
You _can’t_ always know what you could prefer when your call fail.  
Should “stuff” be nil, 0, empty string, new object ?

I suggest you use that in your project (if that’s a big one) and then  
tell us in a few weeks/months if that changed your life or not. If  
that made your debugging harder.  
Then again, this is a matter of personal preference I guess 😉

---

<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 4:16pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/5 "2007-03-21T16:16:42Z")

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On Mar 21, 2007, at 9:04 AM, David A. Black wrote:

> No, I don’t like it. It’s unidiomatic for a ?-method to take a block,

No opinion on nil? but there are a couple examples of ?-methods  
with blocks in core: any?, all?.

Gary W.

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<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 4:33pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/6 "2007-03-21T16:33:46Z")

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On 3/21/07, Gary W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> No opinion on nil? but there are a couple examples of ?-methods  
> with blocks in core: any?, all?.

Agreed. However, the methods you mention use the block in order  
determine whether the predicate is satisfied or not. The action bit  
is still just returning true or false.

The proposed ‘nil?’ uses the block to dispatch some unrelated  
behavior, and it doesn’t return a boolean. I agree with David, et al.  
on this one.

---

<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 2:53pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/7 "2007-03-21T14:53:00Z")

</div>

Michiel De mare wrote:

> If “nil?” is extended to accept a block, and to return self (for  
> Object) and the result of the yield (for NilClass), the following  
> notation becomes possible:
> 
> user.personal\_data.address.nil?{ raise ‘no address!’}.zipcode

Why not use Object#tap?

user.p\_data.address.tap {|a| raise “no address!” unless a}.zipcode

It’s included in Ruby 1.9, is easily definable otherwise  
([http://rubyurl.com/eG5](http://rubyurl.com/eG5)) and does basically what you want.

best,  
Dan

---

<div class="post-metadata">

**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 9:18pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/8 "2007-03-21T21:18:35Z")

</div>

On Wed, Mar 21, 2007 at 09:55:07PM +0900, Michiel de Mare wrote:

> end
> 
> If “nil?” is extended to accept a block, and to return self (for  
> Object) and the result of the yield (for NilClass), the following  
> notation becomes possible:
> 
> user.personal\_data.address.nil?{ raise ‘no address!’}.zipcode

If your result set doesn’t include ‘false’, then you can use ‘or’. Mind  
you,  
it gets ugly with the necessary brackets:

(user.personal\_data.address or raise “no address!”).zipcode

Especially if you go to multiple levels. It looks a bit too much like  
LISP…

(((user or raise “no user!”).  
personal\_data or raise “no personal\_data!”).  
address or raise “no address!”).zipcode

Regards,

Brian.

---

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**Author:** ![mdemare](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/bbe5ce/32.png) [@mdemare](https://www.ruby-forum.com/u/mdemare)\
**Post date:** [March 21, 2007, 4:49pm UTC](https://www.ruby-forum.com/t/nil-with-block/89595/9 "2007-03-21T16:49:48Z")

</div>

On 3/21/07, Michiel de Mare [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> user.personal\_data.address.nil?{ raise ‘no address!’}.zipcode

Instead of interrupting the main flow of code with error handling, how  
about  
this:

begin  
zipcode = user.personal\_data.address.zipcode  
rescue NoMethodError =\> error  
case error  
when :personal\_data then raise “No user!”  
when :address then raise “No personal data!”  
when :zipcode then raise “No address!”  
end

In fact, thanks for spurring me to think of that technique, I think I’m  
going to use it in future!