variable assignment with switch in coffescript

Question

How to use switch for assignment in coffescript? Tried many ways but couldn't make it work.

item = { name: "ahola" }
arr = "coffee_script"

switch arr
 when arr.match /script/
   item.type = arr

 alert item.name + " : " + item.type
 # alerts  "ahola : undefined"

even this doesn't work

item = { name: "ahola" }
arr = "coffee_script"

switch arr
 when arr == "coffee_script"
   item.type = arr

alert item.name + " : " + item.type
# alerts  "ahola : undefined"

tried this way also

item = { name: "ahola" }
arr = "coffee_script"

item.type = switch arr
 when arr.match /script/
   arr

alert item.name + " : " + item.type
# alerts  "ahola : undefined"

At last found this also doesn't work

item = { name: "ahola" }
arr = "coffee_script"

item.type = switch arr
 when true
   arr

alert item.name + " : " + item.type
# alerts  "ahola : undefined"

Am I missing something?

Answer 1

There are two forms of switch in CoffeeScript:

switch expr
  when expr1
    result1
  ...
  else
    default_result

and

switch
  when expr1
    result1
  ...
  else
    default_result

Both forms are, of course, expressions so you can say:

x = switch expr
  when val then result
  ...

and

x = switch
  when expr then result
  ...

The switch expr is like a JavaScript switch: you compare the result of expr with each when expression and execute the when that is == to expr. This form of switch is the same as:

if(expr == expr1)
  result1
else if(expr == expr2)
  result2
...
else
  default_result

The switch ... when form executes the first when expr where expr is true so it is a fancy way of saying:

if(expr1)
  result1
else if(expr2)
  result2
...
else
  default_result

All of your attempts appear to be trying to mix the two forms of switch and confusion ensues.

I think you're looking for something like this:

arr = "coffee_script"
switch arr
  when 'coffee_script'
    item.type = arr
  ...