OpenEuphoria

Re: How to use switch with ranges?

• Posted by DerekParnell (admin) Sep 21, 2010
• 1217 views

switch age do 
     case 1..20 then msg = "No Beer!" 
     case 21..30 then msg = "check dress code" 
     case 31..50 then msg = "suggest they try the veal" 
     case 50.. 

There is a proposal to enhance the switch syntax to cater for some common shorthand sets but it is not likely to make the initial v4 release. However for now you can use the longhand way of doing this, but with the number of cases you are suggesting, it might be slower than a simple 'if' statement ...

switch age do 
     case 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 then msg = "No Beer!" 

The proposed syntax enhancements are ...

  case x to y [by z] then -- Similar to the 'for' statement 
  case in s then -- where the target value is an element of the sequence 's' 

But remember that these are only proposals and are not certain to ever implemented. The purposes of the switch statement include being a faster if statement for non-trivial sets of values so if these proposals can't be implemented as being faster than the equivalent 'if' they might not make it into the language.

The current switch is sort of equivalent to this ...

procedure age_case_A() 
msg = "No Beer!"  
end procedure 
 
procedure age_case_B() 
msg = "check dress code"  
end procedure 
 
procedure age_case_C() 
msg = "suggest they try the veal"  
end procedure 
 
constant ages = {1,2,3,4,5,6,7,8,9,10,11 ... 50} 
constant ageproc = {routine_id("age_case_A"), ... routine_id("age_case_C")} 
res = find(age, ages) 
if res then 
   call_proc( ageproc[res], {}) 
else 
   -- do 'case else' stuff 
end if 

So you could do something similar for your situation, maybe using maps.

procedure age_case_A() 
msg = "No Beer!"  
end procedure 
 
procedure age_case_B() 
msg = "check dress code"  
end procedure 
 
procedure age_case_C() 
msg = "suggest they try the veal"  
end procedure 
 
procedure age_case_else() 
msg = "???"  
end procedure 
 
object agemap = map:new() 
procedure init_age_map() 
 -- Only run once at application start up. 
 for i = 1 to 20 do 
   map:put(agemap, i, routine_id("age_case_A")) 
 end for 
 for i = 21 to 30 do 
   map:put(agemap, i, routine_id("age_case_B")) 
 end for 
 for i = 31 to 50 do 
   map:put(agemap, i, routine_id("age_case_C")) 
 end for 
end procedure 
 
... 
-- When you need to test the 'age' var. 
res = map:get(agemap, age, routine_id("age_case_else")) 
call_proc( res, {}) 

But if I were coding this today I'd use an 'if' ...

if age < 1 then 
   msg = "???" 
elsif age < 21 then 
   msg = "No beer" 
elsif age < 31 then 
   msg = "check dress code" 
elsif age < 51 then 
   msg = "suggest they try the veal" 
else 
   msg = "???" 
end if