Beginner's question: assigning same value to many variables

ruby-talk
1

I'm just starting out in programming, using Ruby to learn.

I'm trying to write a short program that will use a handful of
variables, and I want to be sure that all of the variables start with
the value '' (strings of zero length).

Is there a way to list all of the variables on a single line and set
them to the same value? I tried using commas to seperate, but that
didn't work.

I also tried creating an array with all of the variable names and then
using "arrayname.each do |name|" to cycle through the assignment, but
since the varibles hadn't been defined, I got an "undefined local
variable or method" error (at least, I think that's why I got an error).

···

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Posted via http://www.ruby-forum.com/.

2

a=b=c=d=f=g=h=i=j=k=l=m=n=''

···

On 8/11/06, Alex Khere <askhere@yahoo.com> wrote:

I'm just starting out in programming, using Ruby to learn.

I'm trying to write a short program that will use a handful of
variables, and I want to be sure that all of the variables start with
the value '' (strings of zero length).

Is there a way to list all of the variables on a single line and set
them to the same value? I tried using commas to seperate, but that
didn't work.

I also tried creating an array with all of the variable names and then
using "arrayname.each do |name|" to cycle through the assignment, but
since the varibles hadn't been defined, I got an "undefined local
variable or method" error (at least, I think that's why I got an error).

--
Posted via http://www.ruby-forum.com/\.

--
Mark Van Holstyn
mvette13@gmail.com
http://lotswholetime.com

3

Alex Khere wrote:

I'm just starting out in programming, using Ruby to learn.

I'm trying to write a short program that will use a handful of
variables, and I want to be sure that all of the variables start with
the value '' (strings of zero length).

Is there a way to list all of the variables on a single line and set
them to the same value? I tried using commas to seperate, but that
didn't work.

I also tried creating an array with all of the variable names and then
using "arrayname.each do |name|" to cycle through the assignment, but
since the varibles hadn't been defined, I got an "undefined local
variable or method" error (at least, I think that's why I got an error).

In ruby there are no statements, just expressions. Therefore:

@a = @b = 0

The one caveat, though, is that the references are the same
which means that, for example, assigning "hello" this way
might lead to some confusing results.

Some alternatives include:

@a, @b = 0, 0

@a, @b = Array.new(2) {"Hello"}

Another popular idiom is to defer the initialisation to the
point of first use of the variable. For this the || operator
is often used:

do_something_with(@a || default_value)

do_something_else_with(@b ||= other_default)

The latter operator is shorthand for (@b = @b || default) which
will also assign the default to @b for future use.

···

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Posted via http://www.ruby-forum.com/\.

4

I presume you want each variable initialized to a _different_ empty string. If so, I can't think of an easy way to do it using local variables. That may just go to show my lack of ruby smarts. However, it's not too hard to initialize a group of instance variables to different empty strings in one line of code. Consider:

#! /usr/bin/ruby -w

class Foo
    def initialize
       %w[@a @b @c @d].each {|v| instance_variable_set(v, '')}
    end
end

foo = Foo.new
p foo #=> #<Foo:0x2556c @c="", @b="", @a="", @d="">

And the following will work for global variables.

%w[$a, $b, $c, $d].each {|v| eval("%s=String.new" % v)}
p [$a, $b, $c, $d] #=> ["", "", "", ""]

But for local variables, I don't know.

Regards, Morton

···

On Aug 11, 2006, at 7:12 PM, Alex Khere wrote:

I'm just starting out in programming, using Ruby to learn.

I'm trying to write a short program that will use a handful of
variables, and I want to be sure that all of the variables start with
the value '' (strings of zero length).

Is there a way to list all of the variables on a single line and set
them to the same value? I tried using commas to seperate, but that
didn't work.

I also tried creating an array with all of the variable names and then
using "arrayname.each do |name|" to cycle through the assignment, but
since the varibles hadn't been defined, I got an "undefined local
variable or method" error (at least, I think that's why I got an error).

5

or you could do

%w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

···

On 8/11/06, Mark Van Holstyn <mvette13@gmail.com> wrote:

a=b=c=d=f=g=h=i=j=k=l=m=n=''

On 8/11/06, Alex Khere <askhere@yahoo.com> wrote:
>
> I'm just starting out in programming, using Ruby to learn.
>
> I'm trying to write a short program that will use a handful of
> variables, and I want to be sure that all of the variables start with
> the value '' (strings of zero length).
>
> Is there a way to list all of the variables on a single line and set
> them to the same value? I tried using commas to seperate, but that
> didn't work.
>
> I also tried creating an array with all of the variable names and then
> using "arrayname.each do |name|" to cycle through the assignment, but
> since the varibles hadn't been defined, I got an "undefined local
> variable or method" error (at least, I think that's why I got an error).
>
> --
> Posted via http://www.ruby-forum.com/\.
>

--
Mark Van Holstyn
mvette13@gmail.com
http://lotswholetime.com

--
Mark Van Holstyn
mvette13@gmail.com
http://lotswholetime.com

6

Hi --

···

On Sat, 12 Aug 2006, Mark Van Holstyn wrote:

On 8/11/06, Alex Khere <askhere@yahoo.com> wrote:

I'm just starting out in programming, using Ruby to learn.

I'm trying to write a short program that will use a handful of
variables, and I want to be sure that all of the variables start with
the value '' (strings of zero length).

Is there a way to list all of the variables on a single line and set
them to the same value? I tried using commas to seperate, but that
didn't work.

I also tried creating an array with all of the variable names and then
using "arrayname.each do |name|" to cycle through the assignment, but
since the varibles hadn't been defined, I got an "undefined local
variable or method" error (at least, I think that's why I got an error).

a=b=c=d=f=g=h=i=j=k=l=m=n=''

But beware:

   a=b=c=''
   a << "hi"
   puts b # hi

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
   ----> SEE SPECIAL DEAL FOR RUBY/RAILS USERS GROUPS! <-----
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
Ruby for Rails => book, Ruby for Rails
http://www.rubycentral.org => Ruby Central, Inc.

7

Eero Saynatkari wrote:

In ruby there are no statements, just expressions. Therefore:

@a = @b = 0

The one caveat, though, is that the references are the same
which means that, for example, assigning "hello" this way
might lead to some confusing results...

Thank you, the first example will probably work in this case, but I can
experiment with your other examples.

···

--
Posted via http://www.ruby-forum.com/\.

8

From: Morton Goldberg [mailto:m_goldberg@ameritech.net]
Sent: Friday, August 11, 2006 9:21 PM
To: ruby-talk ML
Subject: Re: Beginner's question: assigning same value to
many variables

I presume you want each variable initialized to a _different_ empty
string. If so, I can't think of an easy way to do it using local
variables. That may just go to show my lack of ruby smarts. However,
it's not too hard to initialize a group of instance variables to
different empty strings in one line of code. Consider:

#! /usr/bin/ruby -w

class Foo
    def initialize
       %w[@a @b @c @d].each {|v| instance_variable_set(v, '')}
    end
end

foo = Foo.new
p foo #=> #<Foo:0x2556c @c="", @b="", @a="", @d="">

And the following will work for global variables.

%w[$a, $b, $c, $d].each {|v| eval("%s=String.new" % v)}
p [$a, $b, $c, $d] #=> ["", "", "", ""]

But for local variables, I don't know.

How about this:

irb(main):001:0> a, b, c = Array.new(3) { '' }
=> ["", "", ""]
irb(main):002:0> a
=> ""
irb(main):003:0> b
=> ""
irb(main):004:0> c
=> ""
irb(main):005:0> a.object_id
=> 203740
irb(main):006:0> b.object_id
=> 203730
irb(main):007:0> c.object_id
=> 203720
irb(main):008:0>

It will work for global and instance variables as well.

Best,
Gennady.

···

-----Original Message-----

Regards, Morton

On Aug 11, 2006, at 7:12 PM, Alex Khere wrote:

> I'm just starting out in programming, using Ruby to learn.
>
> I'm trying to write a short program that will use a handful of
> variables, and I want to be sure that all of the variables
start with
> the value '' (strings of zero length).
>
> Is there a way to list all of the variables on a single line and set
> them to the same value? I tried using commas to seperate, but that
> didn't work.
>
> I also tried creating an array with all of the variable
names and then
> using "arrayname.each do |name|" to cycle through the
assignment, but
> since the varibles hadn't been defined, I got an "undefined local
> variable or method" error (at least, I think that's why I got an
> error).

9

Mark Van Holstyn wrote:

%w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

Isn't that considered _evil_? Using eval on a string, that is.

10

Hi --

···

On Sat, 12 Aug 2006, Mark Van Holstyn wrote:

or you could do

%w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

That won't work; they'll go out of scope. Actually out of two scopes:
the eval scope, and the #each block scope.

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
   ----> SEE SPECIAL DEAL FOR RUBY/RAILS USERS GROUPS! <-----
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
Ruby for Rails => book, Ruby for Rails
http://www.rubycentral.org => Ruby Central, Inc.

11

I like it. I's a much better idea than either of mine.

Regards, Morton

···

On Aug 12, 2006, at 2:39 AM, Gennady Bystritsky wrote:

irb(main):001:0> a, b, c = Array.new(3) { '' }
=> ["", "", ""]
irb(main):002:0> a
=> ""
irb(main):003:0> b
=> ""
irb(main):004:0> c
=> ""
irb(main):005:0> a.object_id
=> 203740
irb(main):006:0> b.object_id
=> 203730
irb(main):007:0> c.object_id
=> 203720
irb(main):008:0>

It will work for global and instance variables as well.

Best,
Gennady.

12

Maybe we should call it "evil" instead of "eval", then.

···

On Sat, Aug 12, 2006 at 08:45:43AM +0900, Suraj N. Kurapati wrote:

Mark Van Holstyn wrote:
> %w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

Isn't that considered _evil_? Using eval on a string, that is.

--
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
"The ability to quote is a serviceable
substitute for wit." - W. Somerset Maugham

13

. . . which is great if you're trying to construct a closure, but not so
great otherwise.

···

On Sat, Aug 12, 2006 at 08:57:37AM +0900, dblack@wobblini.net wrote:

On Sat, 12 Aug 2006, Mark Van Holstyn wrote:

>or you could do
>
>%w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

That won't work; they'll go out of scope. Actually out of two scopes:
the eval scope, and the #each block scope.

--
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
"The measure on a man's real character is what he would do
if he knew he would never be found out." - Thomas McCauley

14

sender: "Morton Goldberg" date: "Sun, Aug 13, 2006 at 02:18:16AM +0900" <<<EOQ

I like it. I's a much better idea than either of mine.

Regards, Morton

>irb(main):001:0> a, b, c = Array.new(3) { '' }

Or even a bit shorter:

a, b, c = Array.new(3,'') OR
a, b, c = [''] * 3

Cheers,
Alex

···

On Aug 12, 2006, at 2:39 AM, Gennady Bystritsky wrote:

15

Hi --

···

On Sat, 12 Aug 2006, Chad Perrin wrote:

On Sat, Aug 12, 2006 at 08:57:37AM +0900, dblack@wobblini.net wrote:

On Sat, 12 Aug 2006, Mark Van Holstyn wrote:

or you could do

%w{ a b c d e f g h i j }.each {|v| eval "#{v}=''" }

That won't work; they'll go out of scope. Actually out of two scopes:
the eval scope, and the #each block scope.

. . . which is great if you're trying to construct a closure, but not so
great otherwise.

I don't think it's ever good for variables you want to use to be out
of scope :slight_smile:

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
   ----> SEE SPECIAL DEAL FOR RUBY/RAILS USERS GROUPS! <-----
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
Ruby for Rails => book, Ruby for Rails
http://www.rubycentral.org => Ruby Central, Inc.

16

No, that doesn't work. We want each variable initialized to a _different_ empty string.

a, b, c, d = Array.new(4) { '' }
p [a, b, c, d].collect {|i| i.object_id} #=> [74020, 74010, 74000, 73990]

a, b, c, d = Array.new(4,'')
p [a, b, c, d].collect {|i| i.object_id} #=> [73920, 73920, 73920, 73920]

a, b, c, d = [''] * 4
p [a, b, c, d].collect {|i| i.object_id} #=> [73820, 73820, 73820, 73820]

Regards, Morton

···

On Aug 12, 2006, at 1:48 PM, Alexandru E. Ungur wrote:

a, b, c = Array.new(3,'') OR
a, b, c = [''] * 3