How to do foo.chomp!.rstrip!.downcase!?

Ruby
#1

Rather than:

foo.chomp!
foo.rstrip!
foo.downcase!

…it seems like I should be able to do:

foo.chomp!.rstrip!.downcase!

…but I get: undefined method `downcase!’ for nil:NilClass
(NoMethodError)

This is probably a basic ruby thing that I’m not grokking…

Many thanks in advance,

  • d
#2

What you’re likely running into is that .rstrip! returns nil if no
change was made.

Check this for more details:
http://ruby-doc.org/core/classes/String.html#M000829

-Alex

#3

Hi –

On Fri, 10 Sep 2010, Geometric Patterns wrote:

…but I get: undefined method `downcase!’ for nil:NilClass
(NoMethodError)

This is probably a basic ruby thing that I’m not grokking…

A lot of destructive ! methods return nil if the object isn’t changed –
for example:

“abc”.gsub!(/z/, “y”)
=> nil

So it’s generally best not to chain them.

David

–
David A. Black, Senior Developer, Cyrus Innovation Inc.

The Ruby training with Black/Brown/McAnally
Compleat Philadelphia, PA, October 1-2, 2010
Rubyist http://www.compleatrubyist.com

#4

Geometric Patterns wrote:

Rather than:

foo.chomp!
foo.rstrip!
foo.downcase!

You could do:

foo.instance_eval { chomp!; rstrip!; downcase! }

#5

Alex S. wrote:

What you’re likely running into is that .rstrip! returns nil if no
change was made.

Check this for more details:
http://ruby-doc.org/core/classes/String.html#M000829

-Alex

Thank you David and Alex!

#6

On 10 Sep, 09:31, Brian C. [email protected] wrote:

foo.instance_eval { chomp!; rstrip!; downcase! }

Posted viahttp://www.ruby-forum.com/.

…or just don’t use the “bang” versions of the methods:

foo = foo.chomp.rstrip.downcase

/lasso

#7

At 2010-09-09 08:23PM, “Geometric Patterns” wrote:

Rather than:

foo.chomp!
foo.rstrip!
foo.downcase!

chomp is not necessary if followed by rstrip.

#8

On Sep 10, 2010, at 11:28 AM, ara.t.howard wrote:

%w( chomp! rstrip! downcase! ).each{|m| foo.send(m)}

-a

So… what’s wrong with:

foo = foo.chomp.rstrip.downcase

Jason

#9

…it seems like I should be able to do:

foo.chomp!.rstrip!.downcase!

you can.

%w( chomp! rstrip! downcase! ).each{|m| foo.send(m)}

-a

#10

On Fri, Sep 10, 2010 at 11:26 AM, Jason R.
[email protected]wrote:

Jason

What is the rationale behind having them return nil if unchanged?

#11

On Fri, Sep 10, 2010 at 6:26 PM, Jason R. [email protected]
wrote:

you can.

%w( chomp! rstrip! downcase! ).each{|m| foo.send(m)}

-a

So… what’s wrong with:

foo = foo.chomp.rstrip.downcase

Each call creates a copy of the string, and are all discarded along
with the original except the last one.

Jesus.

#12

On Fri, Sep 10, 2010 at 8:49 PM, Jason R. [email protected]
wrote:

So… what’s wrong with:

The ! versions don’t work chained, this version does. You shouldn’t be worrying about the cost of creating 3 strings.

I know, regarding that, I don’t see any problem either with

foo.chomp!
foo.rstrip!
foo.downcase!

Robert commented on this already (although his email was lost in some
problem with SpamAssassin, but he resent):

Robert K. wrote:

… which usually is less efficient. I guess OP had a reason to
use bang versions.

and I clarified. If it’s three strings, no problem. If this is in a
loop you might want to reduce garbage. Just pointing out a fact about
the non-bang methods.

Jesus.

#13

On 10 Sep, 23:11, Jesús Gabriel y Galán [email protected]
wrote:

you can.
with the original except the last one.
foo.rstrip!
loop you might want to reduce garbage. Just pointing out a fact about
the non-bang methods.

Jesus.

Yeah, looking at the source code for ruby 1.9 reveals that
String.chomp is essentially implemented as String.sup.chomp!, so
you’re absolutely right about the non bang versions creating some
extra garbage. The same is true about (rstrip and downcase as well.)
How this affects the overall performance is really hard to say without
benchmarking though. But as Robert claimed

foo.chomp!
foo.rstrip!
foo.downcase!

is probable the most efficient way.

/lasso

#14

On Sep 10, 2010, at 1:29 PM, Jesús Gabriel y Galán wrote:

foo = foo.chomp.rstrip.downcase

Each call creates a copy of the string, and are all discarded along
with the original except the last one.

Jesus.

I don’t see any problem there, that’s expected. Ruby has a GC, and those
will get cleaned up appropriately.

The ! versions don’t work chained, this version does. You shouldn’t be
worrying about the cost of creating 3 strings.

Jason

#15

On 12 Sep, 15:13, Lars O. [email protected] wrote:

So… what’s wrong with:
The ! versions don’t work chained, this version does. You shouldn’t be worrying about the cost of creating 3 strings.
Robert K. wrote:
String.chomp is essentially implemented as String.sup.chomp!, so

/lasso

Argh…it was supposed to read “implemented as String.dup.chomp!”

/lasso