Switch statment with empty control expression defaults to false

[OnesimusUnbound]

# CS
switch 
   when "A" then console.log "Hi"
   else console.log "Bye"

// Generated JS
switch (false) {  
  case !"A":    
    console.log("Hi");    
    break;  
  default:    
    console.log("Bye");
 }

CS should report this as an invalid syntax.

Also, I find it strange that ! is prepend for all values in case statament in generated JS.

sample

[gkz]

This is on purpose and useful. You are switching on true - a nice replacement for a series of if-else statements. It compiles to switching on false as it is slightly shorter to cast each of the cases to a boolean with a single ! rather than !!.

[OnesimusUnbound]

@gkz Hmm, I see.

[enable, alerted] = [off, on]
switch 
  when enable then alert "Enabled"
  when alerted then alert "Altered"
  else alert "Normal"

However, don't see ths documented on the official site.

[michaelficarra]

It's intentional and undocumented. There's already an issue open that mentions that this needs to be documented. See #1808. @gabehollombe volunteered to improve the documentation.

[OnesimusUnbound]

I was thinking of a good case of empty switch as part of documenting this feature and I think that it's does better in conditional assignment of value, which improves redability due to use of indent, unlike in if else.

# using switch
score = 90
grade = switch
   when score >= 97 then "A+"
   when score >= 94 then "A"
   when score >= 90 then "A-"
   when score >= 87 then "B+"
   when score >= 84 then "B"
   when score >= 80 then "B-"
   when score >= 78 then "C"
   when score >= 75 then "D"
   else                  "F"

alert grade

# using if else
score = 90
grade = if score >= 97 then "A+"
else if score >= 94 then "A"
else if score >= 90 then "A-"
else if score >= 87 then "B+"
else if score >= 84 then "B"
else if score >= 80 then "B-"
else if score >= 78 then "C"
else if score >= 75 then "D"
else                  "F"

alert grade

[gabehollombe]

Yep, that's a great example. Do you want me to just go with that, and
polish it a bit with some context and wordsmithing?

On Wed, Jul 4, 2012 at 10:56 AM, OnesimusUnbound <
[email protected]

wrote:

I was thinking of a good case of empty switch as part of documenting this
feature and I think that it's does better in conditional assignment of
value, which improves redability due to use of indent, unlike in if else.

# using switch
score = 90
grade = switch
   when score >= 97 then "A+"
   when score >= 94 then "A"
   when score >= 90 then "A-"
   when score >= 87 then "B+"
   when score >= 84 then "B"
   when score >= 80 then "B-"
   when score >= 78 then "C"
   when score >= 75 then "D"
   else                  "F"

alert grade

# using if else
score = 90
grade = if score >= 97 then "A+"
else if score >= 94 then "A"
else if score >= 90 then "A-"
else if score >= 87 then "B+"
else if score >= 84 then "B"
else if score >= 80 then "B-"
else if score >= 78 then "C"
else if score >= 75 then "D"
else                  "F"

alert grade

---

Reply to this email directly or view it on GitHub:
#2416 (comment)

[OnesimusUnbound]

@gabehollombe sure, go ahead ;-)

[gabehollombe]

Pull request is in: #2417