Re: switch revisited

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

If your point is that there are two kinds of switches (those returning 
a value, and those not) you're right.  In C they're explicitly separate 
(switch..case and cond?val : cond2?:val2 ...).  In my proposal, they 
share the same 'switch' term, but it makes little sense for the 
application coder to blend the two types.

Anyways, 'switch' is mainly for C/C++ comers, who don't yet feel very 
comfortable with lookup tables alone.  And, a convenient thing for 
cmdline parameters s.a. below:

	while argv[i] do
        if switch( argv[i], {
            ["-width"]= do width = tonumber(argv[i+1]); i= i+1 end,
            ["-height"]= do height = tonumber(argv[i+1]); i= i+1 end,
		    ["-fullscreen"]= do videoflags= videoflags..SDL_FULLSCREEN end,
		    } ) == nil
        then    -- default
            print("Usage: main_program [-width N] [-height N] 
[-fullscreen]\n")
	       	os.exit(1)
        end
        i= i+1
	end

You are probably right that constant values could be banned completely. 
 But I won't do that just yet. :)

My benefits (compared to other switch alternatives I've seen) are 
mainly the shortened "do .. end" syntax, and the ability to take 
default handling completely outside of the switch structure.

-ak


10.4.2005 kello 01:57, Ben Sunshine-Hill kirjoitti:

 On Apr 9, 2005 12:48 PM, Asko Kauppi <asko.kauppi@sci.fi> wrote:
> >     if type(v)=="function" then
> >         local v2= v()  -- do we get a return value?
> >         if v2~=nil then
>
> I'm a little leery of the special treatment of functions, and
> specifically of functions returning values, here. Seems like it could
> lead to nasty side effects... up until now, adding return values to an
> existing Lua function generally hasn't had any side effects on
> well-written preexisting code. I understand the increased notational
> convenience, but the case of someone needing a switch statement where
> some branches return constants and some execute functions is probably
> rare. I suggest forcing everything to be function-like and have people
> return constants from closures, or not executing anything in a switch
> statement (which makes it into a simple table).
>
> Ben