Beginner's question: assigning same value to many variables

[Alex Khere]

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).

 

[Eero Saynatkari]

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.

 

[Suraj N. Kurapati]

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%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.
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[dblack]

Hi --

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

But beware:

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


David

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http://www.rubycentral.org => Ruby Central, Inc.

 

[Alex Khere]

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.

 

[Chad Perrin]

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

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

 

[dblack]

Hi --

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
http://www.manning.com/black => book, Ruby for Rails
http://www.rubycentral.org => Ruby Central, Inc.

 

[Chad Perrin]

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.

 

[dblack]

Hi --

. . . 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


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
http://www.manning.com/black => book, Ruby for Rails
http://www.rubycentral.org => Ruby Central, Inc.

 

[Morton Goldberg]

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

 

[Gennady Bystritsky]

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

From: Morton Goldberg [mailto:[email protected]]=20
Sent: Friday, August 11, 2006 9:21 PM
To: ruby-talk ML
Subject: Re: Beginner's question: assigning same value to=20
many variables
=20
I presume you want each variable initialized to a _different_ empty =20
string. If so, I can't think of an easy way to do it using local =20
variables. That may just go to show my lack of ruby smarts. However, =20
it's not too hard to initialize a group of instance variables to =20
different empty strings in one line of code. Consider:
=20
#! /usr/bin/ruby -w
=20
class Foo
def initialize
%w[@a @b @c @d].each {|v| instance_variable_set(v, '')}
end
end
=20
foo =3D Foo.new
p foo #=3D> #<Foo:0x2556c @c=3D"", @b=3D"", @a=3D"", @d=3D"">
=20
And the following will work for global variables.
=20
%w[$a, $b, $c, $d].each {|v| eval("%s=3DString.new" % v)}
p [$a, $b, $c, $d] #=3D> ["", "", "", ""]
=20
But for local variables, I don't know.

How about this:

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

It will work for global and instance variables as well.

Best,=20
Gennady.

 

[Morton Goldberg]

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

Regards, Morton

 

[Alexandru E. Ungur]

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

Or even a bit shorter:

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

Cheers,
Alex

 

[Morton Goldberg]

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