Re: switch revisited

[Asko Kauppi <asko.kauppi@...>]

sorry.. here's the code :o

-----
-- switch construct
--
-- Switch and Lua:  http://lua-users.org/wiki/SwitchStatement
--
-- AK/9-Apr-05: Modified so that 'case' keyword is not required
--              (should also be faster due to less table creation & 
direct lookup).
--
-- Usage:
--      switch( action, {
--              [DOG_BARK]= do print "Arf!!!" end,
--              [DOG_BITE]= do print "Chomp!" end,
--              [DOG_SLEEP]= do print "Zzzzzz..." end,
--              } ) or print "Default!"
--
-- Note: Use of 'do' above equals 'function()', if "DO_PATCH" is 
applied.
--       For vanilla Lua 5.x, use the longer "function()".
--
-- Note: Functions are automatically called by 'switch', if they return 
'nil' 
--       the function itself is passed on as the value of 'switch'. 
This allows
--       using "or" for the default (as above).
--
-- Note: Unlike C's 'switch/case' statement, this actually provides the 
value,
--       too, so it can be used in the way "cond1 ? val1 : cond2 ? val2 
: ..."
--       is used in C.  Two flies with one stroke. :)
--
-- Note: The 'key' used may be of any Lua data type.
--
-- WARN: giving a 'false' value in some of the cases will mess up "or" 
usage
--       for default handling. However, "~=nil or ..." will work even 
then.
--
function switch( key, cases )
    --
    assert(key, "nil key in 'switch'")
    local v= cases[key]

    if type(v)=="function" then
        local v2= v()  -- do we get a return value?
        if v2~=nil then
            return v2   -- value returned by the function
        end
    end
    return v	-- nil (or false) will lead to the default (if any)
end


9.4.2005 kello 19:51, Asko Kauppi kirjoitti:


> I revisited the way 'switch' was implemented in LuaX, and here's the 
> code.
>
> This approach is imho more "lua-like" than the earlier, based on Eric 
> Tetz's code was.  Also, it only consumes the "switch" keyword, and 
> uses neither "case" nor "default".
>
> Comments are welcome, but for those not being there the "last time" 
> have a look at 
> http://archive.neotonic.com/archive/lua-l/browse_frm/thread/3024/13494 
>  thread first. :)
>
> (oops, that was the 'continue' thread, but there's some on switch 
> about the same time..)
>
>
> BTW, could "do ... end" be used instead of anonymous non-parameter 
> closures?  has anyone done that:
>
> --      switch( action, {
> --              [DOG_BARK]= do print "Arf!!!" end,
> --              [DOG_BITE]= do print "Chomp!" end,
> --              [DOG_SLEEP]= do print "Zzzzzz..." end,
> --              } ) or print "Default!"
>
> -ak