How to write a switch statement in Ruby

Question

How do I write a switch statement in Ruby

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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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As stated in many of the above answers  the     operator is used under the hood on case when statements  Here is additional information about that operator  Case equality operator      Many of Ruby s built-in classes  such as String  Range  and Regexp  provide their own implementations of the     operator  also known as  quot case-equality quot    quot triple equals quot  or  quot threequals quot   Because it s implemented differently in each class  it will behave differently depending on the type of object it was called on  Generally  it returns true if the object on the right  quot belongs to quot  or  quot is a member of quot  the object on the left  For instance  it can be used to test if an object is an instance of a class  or one of its sub-classes   String      quot zen quot     Output    gt  true Range      1  2      Output    gt  true Array      1 2 3      Output    gt  true Integer     2     Output    gt  true  The same result can be achieved with other methods which are probably best suited for the job  such as is a  and instance of   Range Implementation of     When the     operator is called on a range object  it returns true if the value on the right falls within the range on the left   1  4      3    Output    gt  true  1  4      2 345   Output    gt  true  1  4      6    Output    gt  false    quot a quot    quot d quot        quot c quot    Output    gt  true   quot a quot    quot d quot        quot e quot    Output    gt  false  Remember that the     operator invokes the     method of the left-hand object  So  1  4      3 is equivalent to  1  4      3  In other words  the class of the left-hand operand will define which implementation of the     method will be called  so the operand positions are not interchangeable  Regexp Implementation of     Returns true if the string on the right matches the regular expression on the left   zen       quot practice zazen today quot     Output    gt  true   is similar to  quot practice zazen today quot     zen   The only relevant difference between the two examples above is that  when there is a match      returns true and    returns an integer  which is a truthy value in Ruby  We will get back to this soon

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I ve started to use   a    secondcase   var name   case a   when  firstcase  then  foo    when  secondcase  then  bar  end  puts var name  gt  gt   bar    It helps compact code in some cases

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You can do like this in more natural way   case expression when condtion1    function when condition2    function else    function end

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Since switch case always returns a single object  we can directly print its result   puts case a      when 0          It s zero       when 1          It s one       end

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Multi-value when and no-value case   print  Enter your grade    grade   gets chomp case grade when  A    B    puts  You pretty smart   when  C    D    puts  You pretty dumb    else   puts  You can t even use a computer   end   And a regular expression solution here   print  Enter a string    some string   gets chomp case when some string match   d     puts  String has numbers  when some string match   a-zA-Z      puts  String has letters  else   puts  String has no numbers or letters  end

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You can write case expressions in two different ways in Ruby    Similar to a series of if statements Specify a target next to the case and each when clause is compared to the target    age   20 case  when age  gt   21 puts  display something  when 1    0 puts  omg  else puts  default condition  end   or   case params  unknown  when  Something  then  Nothing  when  Something else  then  I dont know  end

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Many programming languages  especially those derived from C  have support for the so-called Switch Fallthrough  I was searching for the best way to do the same in Ruby and thought it might be useful to others   In C-like languages fallthrough typically looks like this   switch  expression        case  a       case  b       case  c              Do something for a  b or c         break      case  d       case  e              Do something else for d or e         break      In Ruby  the same can be achieved in the following way   case expression when  a    b    c      Do something for a  b or c when  d    e      Do something else for d or e end   This is not strictly equivalent  because it s not possible to let  a  execute a block of code before falling through to  b  or  c   but for the most part I find it similar enough to be useful in the same way

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The case statement operator is like switch in the other languages   This is the syntax of switch   case in C   switch  expression         case constant1           statements       break      case constant2           statements       break                        default           default statements     This is the syntax of case   when in Ruby   case expression   when constant1  constant2  Each when statement can have multiple candidate values  separated by commas         statements       next   is like continue in other languages   when constant3        statements       exit   exit is like break in other languages               else        statements end   For example   x   10 case x when 1 2 3   puts  1  2  or 3    exit when 10   puts  10    it will stop here and execute that line   exit   then it ll exit else   puts  Some other number  end   For more information see the case documentation

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If you are eager to know how to use an OR condition in a Ruby switch case   So  in a case statement  a   is the equivalent of    in an if statement   case car    when  Maruti    Hyundai          Code here end   See  How A Ruby Case Statement Works And What You Can Do With It

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No support for regular expressions in your environment  E g  Shopify Script Editor  April  2018     Error   uninitialized constant RegExp  A workaround following a combination of methods already previously covered in here and here  code     ADD-SUPER-BONUS    class StrContains   def self     item      item include   SUPER  or item include   MEGA  or      item include   MINI  or item include   UBER    end end  case code upcase when  12345PROMO    CODE-007   StrContains   puts  quot Code   code  is a discount code  quot  when   ADD-BONUS     puts  This is a bonus code   else   puts  Sorry  we can  t do anything with the code you added     end  I used ors in the class method statement since    has higher precedence than  include   If you still prefer using     even though or is preferable in this case  you can do this instead   item include   A           You can test it in this repl it

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Depending on your case  you could prefer to use a hash of methods   If there is a long list of whens and each of them has a concrete value to compare with  not an interval   it will be more effective to declare a hash of methods and then to call the relevant method from the hash like that     Define the hash menu    a   menu1  b   menu2  c   menu2  d   menu3     Define the methods def menu1   puts  menu 1  end  def menu2   puts  menu 2  end  def menu3   puts  menu3  end    Let s say we case by selected menu    a selected menu    a    Then just call the relevant method from the hash send menu selected menu

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puts  Recommend me a language to learn   input   gets chomp downcase to s  case input when  ruby      puts  Learn Ruby  when  python      puts  Learn Python  when  java      puts  Learn Java  when  php      puts  Learn PHP  else      Go to Sleep   end

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It s critical to emphasize the comma     in a when clause  It acts as an    of an if statement  that is  it does an OR comparison and not an AND comparison between the delimited expressions of the when clause  See the following case statement   x   3 case x   when 3  x  lt  2 then  apple    when 3  x  gt  2 then  orange  end    gt   apple    x is not less than 2  yet the return value is  apple   Why  Because x was 3 and since      acts as an    it did not bother to evaluate the expressionx  lt  2    You might think that to perform an AND  you can do something like this below  but it doesn t work   case x   when  3  amp  amp  x  lt  2  then  apple    when  3  amp  amp  x  gt  2  then  orange  end    gt  nil    It doesn t work because  3  amp  amp  x  gt  2  evaluates to true  and Ruby takes the True value and compares it to x with      which is not true  since x is 3    To do an  amp  amp  comparison  you will have to treat case like an if else block   case   when x    3  amp  amp  x  lt  2 then  apple    when x    3  amp  amp  x  gt  2 then  orange  end   In the Ruby Programming Language book  Matz says this latter form is the simple  and infrequently used  form  which is nothing more than an alternative syntax for if elsif else  However  whether it is infrequently used or not  I do not see any other way to attach multiple  amp  amp  expressions for a given when clause

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age    5 case  age when 0    2    puts  baby  when 3    6    puts  little child  when 7    12    puts  child  when 13    18    puts  youth  else    puts  adult  end   See  Ruby - if   else  case  unless  for more information

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I prefer to use case   than number   10  case number when 1   8 then       when 8   15 then       when 15   then       end

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case   when behaves a bit unexpectedly when handling classes  This is due to the fact that it uses the     operator   That operator works as expected with literals  but not with classes   1     1               gt  true Fixnum     Fixnum     gt  false   This means that if you want to do a case     when over an object s class  this will not work   obj    hello  case obj class when String   print  It is a string   when Fixnum   print  It is a number   else   print  It is not a string or number   end   Will print  It is not a string or number    Fortunately  this is easily solved  The     operator has been defined so that it returns true if you use it with a class and supply an instance of that class as the second operand   Fixnum     1     gt  true   In short  the code above can be fixed by removing the  class   obj    hello  case obj    was case obj class when String   print  It is a string   when Fixnum   print  It is a number   else   print  It is not a string or number   end   I hit this problem today while looking for an answer  and this was the first appearing page  so I figured it would be useful to others in my same situation

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Lots of great answers but I thought I would add one factoid   If you are attempting to compare objects  Classes  make sure you have a space ship method  not a joke  or understand how they are being compared   Ruby Equality And Object Comparison  is a good discussion on the topic

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It is done using case in Ruby  Also see  Switch statement  on Wikipedia   Quoted   case n when 0   puts  You typed zero  when 1  9   puts  n is a perfect square  when 2   puts  n is a prime number    puts  n is an even number  when 3  5  7   puts  n is a prime number  when 4  6  8   puts  n is an even number  else   puts  Only single-digit numbers are allowed  end   Another example   score   70  result   case score    when 0  40 then  Fail     when 41  60 then  Pass     when 61  70 then  Pass with Merit     when 71  100 then  Pass with Distinction     else  Invalid Score  end  puts result   On around page 123 of The Ruby Programming Language  1st Edition  O Reilly  on my Kindle  it says the then keyword following the when clauses can be replaced with a newline or semicolon  just like in the if then else syntax    Ruby 1 8 also allows a colon in place of then  but this syntax is no longer allowed in Ruby 1 9

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We can write switch statement for multiple conditions    For Example   x   22  CASE x   WHEN 0  14 THEN puts    x  is less than 15        WHEN 15 THEN puts    x  equals 15     WHEN 15 THEN puts    x  equals 15     WHEN 15  20 THEN puts    x  is greater than 15     ELSE puts  Not in the range  value   x     END

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You can use regular expressions  such as finding a type of string   case foo when    true false       puts  Given string is boolean  when    0-9         puts  Given string is integer  when    0-9          puts  Given string is float  else    puts  Given string is probably string  end   Ruby s case will use the equality operand     for this  thanks  JimDeville   Additional information is available at  Ruby Operators   This also can be done using  mmdemirbas example  without parameter   only this approach is cleaner for these types of cases

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It s called case and it works like you would expect  plus lots more fun stuff courtesy of     which implements the tests   case 5   when 5     puts  yes    else     puts  else  end   Now for some fun   case 5   every selector below would fire  if first    when 3  7      OK  this is nice   when 3 4 5 6   also nice   when Fixnum    or   when Integer   or   when Numeric   or   when Comparable        or   when Object     duhh  or   when Kernel         or   when BasicObject    enough already          end   And it turns out you can also replace an arbitrary if else chain  that is  even if the tests don t involve a common variable  with case by leaving out the initial case parameter and just writing expressions where the first match is what you want   case   when x nil            when  x match    fn              when  x include   substring             when x gsub  o    z       fnzrq            when Time now tuesday          end

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Ruby uses the case for writing switch statements   As per the case documentation      Case statements consist of an optional condition  which is in the   position of an argument to case  and zero or more when clauses    The first when clause to match the condition  or to evaluate to   Boolean truth  if the condition is null     wins     and its code stanza   is executed  The value of the case statement is the value of the   successful when clause  or nil if there is no such clause       A case statement can end with an else clause  Each when a   statement can have multiple candidate values  separated by commas    Example   case x when 1 2 3   puts  1  2  or 3  when 10   puts  10  else   puts  Some other number  end   Shorter version   case x when 1 2 3 then puts  1  2  or 3  when 10 then puts  10  else puts  Some other number  end     And as  Ruby s case statement - advanced techniques  describes Ruby case   Can be used with Ranges   case 5 when  1  10    puts  case statements match inclusion in a range  end       gt   case statements match inclusion in a range    Can be used with Regex   case  FOOBAR  when  BAR     puts  they can match regular expressions   end       gt   they can match regular expressions     Can be used with Procs and Lambdas   case 40 when - gt   n    n to s     40      puts  lambdas   end       gt   lambdas    Also  can be used with your own match classes   class Success   def self     item      item status  gt   200  amp  amp  item status  lt  300   end end  class Empty   def self     item      item response size    0   end end  case http response when Empty   puts  response was empty  when Success   puts  response was a success  end

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case   when  To add more examples to Chuck s answer   With parameter   case a when 1   puts  Single value  when 2  3   puts  One of comma-separated values  when 4  6   puts  One of 4  5  6  when 7   9   puts  One of 7  8  but not 9  else   puts  Any other thing  end   Without parameter   case when b  lt  3   puts  Little than 3  when b    3   puts  Equal to 3  when  1  10      b   puts  Something in closed range of  1  10   end   Please  be aware of  How to write a switch statement in Ruby  that kikito warns about

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In Ruby 2 0  you can also use lambdas in case statements  as follows   is even   - gt  x    x   2    0    case number when 0 then puts  zero  when is even then puts  even  else puts  odd  end   You can also create your own comparators easily using a Struct with a custom      Moddable   Struct new  n  do   def     numeric      numeric   n    0   end end  mod4   Moddable new 4  mod3   Moddable new 3   case number when mod4 then puts  multiple of 4  when mod3 then puts  multiple of 3  end    Example taken from  Can procs be used with case statements in Ruby 2 0      Or  with a complete class   class Vehicle   def     another vehicle      self number of wheels    another vehicle number of wheels   end end  four wheeler   Vehicle new 4 two wheeler   Vehicle new 2  case vehicle when two wheeler   puts  two wheeler  when four wheeler   puts  four wheeler  end    Example taken from  How A Ruby Case Statement Works And What You Can Do With It

[ruby] How to write a switch statement in Ruby

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