Newbie : assign a value to a variable

Ruby
1

Hi all!

This is really a newbie question…

Here is the simple code…

if @params[:per_page].nil?
per_page = 20
else
per_page = @params[:per_page]
end

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

Thanks…

Nicolas

2

Hi –

On Mon, 28 Aug 2006, Nicolas B. wrote:

end

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

You can use the || (or) operator:

per_page = @params[:per_page] || 20

David

3

On 8/28/06, Nicolas B. [email protected] wrote:

end

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

#untested:
per_page = (@params[:per_page] or 20)
#The theory is that if @params[:per_page] is nil, it’ll return false,
and the ‘or’ will kick in.

Thanks…

You’re welcome.

Nicolas

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

hmmm,
-Harold

4

Nicolas B. wrote:
…

if @params[:per_page].nil?
per_page = 20
else
per_page = @params[:per_page]
end

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

The usual idiom is
per_page = @params[:per_page] || 20

cheers

5

Try this:

per_page = @params[:per_page] || 20

Best Regards
Maikon Araujo.

6

You can use the || (or) operator:

per_page = @params[:per_page] || 20

David

I think you’ve got to be careful about your precedence there…

irb(main):001:0> foo = nil or 20
=> 20
irb(main):002:0> foo
=> nil
irb(main):003:0> foo = (nil or 20)
=> 20
irb(main):004:0> foo
=> 20

Though, maybe it’s just irb?

-Harold

7

On Aug 28, 2006, at 8:30 AM, Harold H. wrote:

irb(main):001:0> foo = nil or 20
=> 20
irb(main):002:0> foo
=> nil
irb(main):003:0> foo = (nil or 20)
=> 20
irb(main):004:0> foo
=> 20

Though, maybe it’s just irb?

IRb and Ruby treat this the same, but David didn’t use “or” so the
precedence is fine. :wink:

James Edward G. II

8

On 8/28/06, James Edward G. II [email protected] wrote:

Though, maybe it’s just irb?

IRb and Ruby treat this the same, but David didn’t use “or” so the
precedence is fine. :wink:

James Edward G. II

holycrap.

Not to highjack this thread or anything, but what’s the difference
between ‘||’ and ‘or’ ?

Only precedence? Or is ‘or’ some kind of tricky method?

At least we both gave him working code, I guess… haha.

-Harold

9

Hi –

On Mon, 28 Aug 2006, Harold H. wrote:

irb(main):001:0> foo = nil or 20
=> 20
irb(main):002:0> foo
=> nil
irb(main):003:0> foo = (nil or 20)
=> 20
irb(main):004:0> foo
=> 20

Though, maybe it’s just irb?

No, it’s just “or”, which I didn’t use. (Look more closely at my code
:slight_smile:

David

10

Hi –

On Mon, 28 Aug 2006, Harold H. wrote:

=> 20
holycrap.

Not to highjack this thread or anything, but what’s the difference
between ‘||’ and ‘or’ ?

Only precedence? Or is ‘or’ some kind of tricky method?

Only precedence, as far as I know.

David

11

On Aug 28, 2006, at 8:45 AM, Harold H. wrote:

Not to highjack this thread or anything, but what’s the difference
between ‘||’ and ‘or’ ?

“and” and “or” have much lower precedence than “&&” and “||”, mostly
to allow for natural language constructs like:

res = may_return_nil() or raise “Oops, we got a nil!”

Hope that helps.

James Edward G. II

12

Thanks for the trick.

But the next problem is that if params[:per_page] equals 0 then per_page
equals 0 and I get the error message “must have at least one item per
page” from the Rails paginate option…

unknown wrote:

Hi –

On Mon, 28 Aug 2006, Nicolas B. wrote:

end

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

You can use the || (or) operator:

per_page = @params[:per_page] || 20

David

13

On Mon, 28 Aug 2006, Nicolas B. wrote:

Thanks for the trick.

But the next problem is that if params[:per_page] equals 0 then per_page
equals 0 and I get the error message “must have at least one item per
page” from the Rails paginate option…

per_page = @params[:per_page] || 20

In that case, use the trinary operator. Call to_i on @params[:per_page]
if it could be nil, as you don’t want to do that comparison with nil.

per_page = @params[:per_page].to_i > 0 ? @params[:per_page] : 20

Kirk H.

14

On 8/28/06, Nicolas B. [email protected] wrote:

Thanks for the trick.

But the next problem is that if params[:per_page] equals 0 then per_page
equals 0 and I get the error message “must have at least one item per
page” from the Rails paginate option…

per_page = @params[:per_page] || 20 # default
per_page = 20 if per_page <= 0 # validity check

or the other way round:

per_page = @params[:per_page] # assignment
per_page = nil if per_page <= 0 # validity check
per_page ||= 20 # default

Choose what you like best.

15

Thanks!

I tried :
per_page = @params[:per_page].to_i > 0 ? @params[:per_page] : 20

but in this case if @params[:per_page] = ‘blahblah’ it works, I get 20
in per_page but if @params[:per_page] = 6 or another integer I get :
undefined method `>’ for false:FalseClass

from Rails…

Nicolas.

unknown wrote:

On Mon, 28 Aug 2006, Nicolas B. wrote:

Thanks for the trick.

But the next problem is that if params[:per_page] equals 0 then per_page
equals 0 and I get the error message “must have at least one item per
page” from the Rails paginate option…

per_page = @params[:per_page] || 20

In that case, use the trinary operator. Call to_i on @params[:per_page]
if it could be nil, as you don’t want to do that comparison with nil.

per_page = @params[:per_page].to_i > 0 ? @params[:per_page] : 20

Kirk H.

16

On 28 août 06, at 15:30, ChrisH wrote:

The usual idiom is
per_page = @params[:per_page] || 20

You can also do:
per_page = @params.fetch(:per_page, 20)

Or:
@params.default = 20
per_page = @params[:per_page]

17

On 8/28/06, Nicolas B. [email protected] wrote:

  per_page = @params[:per_page]

end

You got very bright answers from very good people, or was it the other
way
round?

The answers were of type
var = val || default_val

As it seems that you are accessing a Hash object, you could do the
following
which is semantically different and this is the main reason I anwser
your
post.

per_page = @params.fetch( :per_page, 20 )

Now where is the difference:

if @params does not contain the key :per_page, 20 is returned, however
if
@params[:per_page] was set to nil or false, nil or false is returned
accordingly

It is up to you to know what you need :slight_smile:

Hope that helps
Robert

Is there a better way to do this (put the parameter in the variable if

the parameter is not null, otherwise put 20) ?

Thanks…

Nicolas

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

–
Deux choses sont infinies : l’univers et la bêtise humaine ; en ce qui
concerne l’univers, je n’en ai pas acquis la certitude absolue.

  • Albert Einstein
18

On Mon, 28 Aug 2006, Nicolas B. wrote:

I tried :
per_page = @params[:per_page].to_i > 0 ? @params[:per_page] : 20

but in this case if @params[:per_page] = ‘blahblah’ it works, I get 20
in per_page but if @params[:per_page] = 6 or another integer I get :
undefined method `>’ for false:FalseClass

from Rails…

???

Can someone tell me what horrible thing Rails is doing to the language,
there?

How is @params[:per_page].to_i becoming false?

Kirk H.

19

Nicolas B. wrote

Is there a better way to do this (put the parameter in the variable if
the parameter is not null, otherwise put 20) ?

The original way works.

Just how much “better” than “works” do you want? I’d say fight the urges
to golf.

David V.

20

Thank you very much for all your answers…

I think I will use this for now :

per_page = @params.fetch(:per_page, 20).to_i
per_page = 20 if per_page <= 0

Nicolas.