Test If Variable Matches Any of Several Strings W/O Long If-Elsif Chain, or Case-When

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

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 )

ruby - How to do if X is equal to either one of these values (xxx,eeee,yyyy,dadadad)

Use a regular expression:

do_x if file_ext =~ /\A(doc|xls|ppt)\Z/

Or, if you have a large enough list of things that writing a regex feels impractical, you could do something like

file_extensions = %w(xls csv doc txt odf jpg png blah blah blah blah blah)
do_x if file_extensions.include?(file_ext)

Of course there is always the option of testing each value individually:

do_x if file_ext == "doc" || file_ext == "xls" || ... || file_ext == "zzz"

In Ruby, how do I find out if a string is not in an array?

do_this unless  ["www", "blog", "foo", "bar"].include?(current_subdomain)

or

do_this if not ["www", "blog", "foo", "bar"].include?(current_subdomain)

I'm using the Array#include? method.

However using unless is a fairly big ruby idiom.

Why doesn't my if/elsif statement create tagged links and send them to different routes?

If you use if/else statements, you want to ask a question and perform one or the other based on the answer. It's called a conditional statement because you want a condition to be met before providing an action. Only after the answer is given you tell what to do next.

Now, what you are doing is the opposite. You tell what to do, without ever asking the question when to do it. No wonder it only runs the if statement, since this statement always returns true. The problem you face is that your first condition can never be false or nil.

As a rule of thumb, a question/condition should always have multiple possible answers, otherwise there is no point in asking.

Ruby case statements with multiple variables

This is a simplistic way to add ===:

class Array
  def ===(other)
    return false if (other.size != self.size)

    other_dup = other.dup
    all? do |e|
      e === other_dup.shift
    end
  end
end

[
  ['foo', 3],
  %w[ foo bar ],
  %w[ one ],
  []
].each do |ary|

  ary_type = case ary
  when [String, Fixnum] then "[String, Fixnum]"
  when [String, String] then "[String, String]"
  when [String] then "[String]"
  else
    "no match"
  end

  puts ary_type

end

# >> [String, Fixnum]
# >> [String, String]
# >> [String]
# >> no match

How to write a switch statement in Ruby

Ruby uses the case expression instead.

case x
when 1..5
  "It's between 1 and 5"
when 6
  "It's 6"
when "foo", "bar"
  "It's either foo or bar"
when String
  "You passed a string"
else
  "You gave me #{x} -- I have no idea what to do with that."
end

Ruby compares the object in the when clause with the object in the case clause using the === operator. For example, 1..5 === x, and not x === 1..5.

This allows for sophisticated when clauses as seen above. Ranges, classes and all sorts of things can be tested for rather than just equality.

Unlike switch statements in many other languages, Ruby’s case does not have fall-through, so there is no need to end each when with a break. You can also specify multiple matches in a single when clause like when "foo", "bar".

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