Add list validator

[matthew342]

I had use for a validator that checks whether an attribute is included in a list of allowed values. I figure this is a pretty common need, so I thought I'd put in a PR.

[matthew342]

Rebased against 0.9.3pre2

[ryanstout]

@matthew342 sorry I haven't gotten back you on this. Been busy finishing off another branch. Should have time for it this weekend.

[ryanstout]

@matthew342 Thanks for this PR, sorry it took me so long to get to it. I went to merge it, but its failing the specs when run in opal (bundle exec rake) Any chance you can see if you can figure out what's going on?

[matthew342]

No problem. Am a bit tied up for the next couple of days, but will take a
look early next week.

On Wed, Jul 29, 2015 at 12:48 AM, Ryan Stout notifications@github.com
wrote:

@matthew342 https://github.com/matthew342 Thanks for this PR, sorry it
took me so long to get to it. I went to merge it, but its failing the specs
when run in opal (bundle exec rake) Any chance you can see if you can
figure out what's going on?

—
Reply to this email directly or view it on GitHub
#212 (comment).

[dennym]

Just out of curiousity, what is a usecase for such a validator?

[matthew342]

Now should be ready to merge.

Rebased on current master and fixed specs in Opal - it was the use of 'params' in a let() that apparently was causing the troubles.

[matthew342]

@dennym Any time you want to validate that a field is a value from an arbitrary list of possible values.

[jfahrer]

@matthew342 Did you consider naming the validator inclusion_validator?

validates :name, inclusion: { in: ['some', 'elements'] }

This might be more intuitive for the people coming from rails

[matthew342]

@jfahrer No, hadn't crossed my mind but makes more sense that way. I'll update this weekend.