From: Robert Klemme <shortcutter@...>
Date: 2008-08-21T20:38:23+09:00
Subject: Re: "num in [1,2,3,4]" in a cool way?

2008/8/21 Martin DeMello <martindemello@gmail.com>:
> On Wed, Aug 20, 2008 at 8:03 PM, Mikael Høilund <mikael@hoilund.org> wrote:
>>
>> num = 5
>> ary.inject(false) { |m, v| true if m or v == num }
>
> or even
>
> ary.inject(false) { |m, v| m or v == num }

Disclaimer: I would not use #inject in this case.

But since you asked...

We can even short circuit with #inject:

irb(main):003:0> i = 3
=> 3
irb(main):004:0> (1..4).inject(nil) {|b,a| break a if i == a}
=> 3
irb(main):005:0> i = 10
=> 10
irb(main):006:0> (1..4).inject(nil) {|b,a| break a if i == a}
=> nil

But then again, you could directly use #find or even better #include?.

If it's for integers I'd probably just do

irb(main):010:0> i = 3
=> 3
irb(main):011:0> i >= 1 && i <= 4
=> true
irb(main):012:0> (1..4) === i
=> true

Here's a different approach:

irb(main):013:0> pat = (1..4).inject(0) {|x,a| x | 1 << a}
=> 30
irb(main):014:0> pat.to_s 2
=> "11110"
irb(main):015:0> pat[i] == 1
=> true

:-)

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end