OpenEuphoria

Re: [DOS] Can we emulate "pass by reference" in Eu?

• Posted by "Christian Cuvier" <Christian.CUVIER at agriculture.gouv.fr> Oct 19, 2004
• 636 views

> 
> posted by: Alex Caracatsanis <CaracatsanisA at ramsayhealth.com.au>
> 
> Dear List
> 
> For my general knowledge, rather than with a specific program in mind, I'd
> like to ask how to pass a non-global variable (two scenario's: an atom; a
> sequence) as an argument to:
> 1 a procedure that changes the variable (eg increments it)
> 2 a function that changes the variable (eg increments it) but returns some
> other, different, variable
> 
> A "minimal" example to achieve the above, would be enough.
> 
> Thank you
> 
> Alex Caracatsanis


Yes:

sequence sharedvars
sharedvars=repeat(0,27) --whatever max limit to the number of shared variables
--extending it dynamically is trickier, see below

procedure proc1(integer passedbyref,object othervars)
object whatever
--some code
sharedvars[passedbyref]=whatever
--...
end procedure

--...
sharedvars[slot]=myarg
proc1(slot,optionallySomethingElse)
--sharedvars[slot] holds the modified value

Replace "procedure" by "function" as needed. After all, that's how the network 
interrupt #5C works.
You have to keep track of slot alloction and return types yourself.

Now some code in order to forget about any max size of sharedvars:

sequence sharedvars sharedvars={0,0,0}
integer usedslots usedslots=0

function allotslot(object x)
if usedslots=length(sharedvars) then sharedvars&=0 end if
usedslots+=1
sharedvars[usedslots]=x
return usedslots
end function
procedure endgame() usedslots=0 end procedure
--...

procedure proc1(integer passedbyref,object othervars)
object whatever
--some code
sharedvars[passedbyref]=whatever
--...
end procedure

integer slot
slot=allotslot(myarg)
proc1(slot,optionallySomethingElse)
--sharedvars[slot] holds the modified value
--...
endgame()  --current tempvars no longer valid, clean up

That's clumsier, but you no longer take care of slots; just remember which 
holds what.
And you can typecheck sharedvars[slot] at any time and take any appropriate 
action.

CChris