Test if variable matches any of several strings w/o long if-elsif chain, or case-when

Question

I assume there is a nice one-line way to say in ruby

if mystr == "abc" or "def " or "ghi" or "xyz"

but cannot find how to do that in the online references I normally consult...

Thanks!

Solution 1

Perhaps you didn't know that you can put multiple conditions on a single case:

case mystr
  when "abc", "def", "ghi", "xyz"
    ..
end

But for this specific string-based test, I would use regex:

if mystr =~ /\A(?:abc|def|ghi|xyz)\z/

If you don't want to construct a regex, and you don't want a case statement, you can create an array of objects and use Array#include? test to see if the object is in the array:

if [a,b,c,d].include?( o )

or, by monkey-patching Object, you can even turn it around:

class Object
  def in?( *values )
    values.include?( self )
  end
end

if o.in?( a, b, c, d )

Solution 2

You can use Array#include? like this:

if ["abc", "def ", "ghi", "xyz"].include?(mystr)

Solution 3

>> mystr="abc"
=> "abc"
>> mystr[/\A(abc|def|ghi|xyz)\z/]
=> "abc"
>> mystr="abcd"
=> "abcd"
>> mystr[/\A(abc|def|ghi|xyz)\z/]
=> nil

Comments

[Jörg W Mittag]

And in this specific case, I would use the whitespace delimited array literal syntax to get rid of all the commas and quotes: %w[abc def ghi xyz].include?(mystr)

[jpw]

what dos the ?: do? (google doesnt let you search for symbols, and the three ruby/regex guides I looked up didnt have : far as I can tell)

[Phrogz]

In a regex you use parentheses to limit an expression and also to capture it for later use. In this case we don't actually need to or want to capture it, so putting ?: at the start of the parentheses is an instruction not to capture it. See the official Oniguruma regex syntax for more information.

[jpw]

because I completely missed the 3rd example you provided, which was the same as the (excellent/succinct) provided by sepp2k. Fixed. It is cool you provided several examples, thx.