ruby: What's the meaning of keyword "in"

Question

When I find the keyword "in" in ruby first time. I think maybe I can do that: 1 in (0..10) But it look like I cannot use it like that way.

Then I search it in ruby-lang.org, and google it. There is no answer!

What's the meaning of keyword "in" in ruby?

See also this question: http://stackoverflow.com/questions/155462/what-is-for-in-ruby — Mark Pim, Jun 18 '09 at 07:40

score 6 · Accepted Answer · answered Jun 18 '09 at 07:43

6

You should be able to do the following:

for i in 0..10 do
  puts i
end

The expression 1 in (0..10) that you mention won't work because a constant (1) can't vary over a range - it's a constant! You need to name a variable before the in keyword.

Hope that helps.

See this page as well.

answered Jun 18 '09 at 07:43

Mark Pim

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Thank you! Because I come from F# and lisp. I always use "each" "map". I even forget the "for" loop keyword. – colder Jun 18 '09 at 08:01
You can also use "for in"-loops in F# – Mouk Jun 18 '09 at 08:41
5

Object#each is probably more Ruby-ish than for...in – Mike Woodhouse Jun 18 '09 at 08:56
3

To achieve the same result from 'for i in 0..10', one could use Fixnum#times i.e. '10.times do |i| ... end'. I think this is indeed more expressive and more "Ruby-ish". – Igor Jun 20 '09 at 08:31

score 0 · Answer 2 · answered Jun 18 '09 at 07:37

0

according to the pragmatic programmers book you se it as following

while *name*[, *name*]... in *expression* [do | :]
  body
end

so you use it in loops, sorry if this is vague, but i have only started learning ruby.

answered Jun 18 '09 at 07:37

Craig

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score 0 · Answer 3 · answered Jul 28 '22 at 10:35

I think maybe I can do that: 1 in (0..10) But it look like I cannot use it like that way

Now you can :)

Because Ruby introduced pattern matching

1 in 0..10 is alias of this code:

case 1
in 0..10
  true
else
  false
end

Using 1 in 0..10 expression you can check if one expression matches another

ruby: What's the meaning of keyword "in"

3 Answers3

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