Hi Victor,

I think I now understand the main difference between the two style approaches, and more generally advantages and limits of the pass by reference concept. Thank you.

The following code works well, but I'm never completely sure of the relevance and the good way in Csound...   
After a quick look nothing lets consider future bugs?
 


-odac 



sr = 44100
ksmps = 128
nchnls = 2
0dbfs  = 1

gisquare ftgen 2, 0, 16384, 10, 1, 0 , .33, 0, .2 , 0, .14, 0 , .11, 0, .09

opcode ctrl(pfield:i):(k)
chnidx:S = sprintf("%.02f_p%d", p1, pfield)
fieldvalue:i = pindex(pfield)
print(fieldvalue)
chnset(fieldvalue,chnidx)
value:k init fieldvalue
value:k = chnget(chnidx)
puts(chnidx, 1)
xout(value)
endop

// ctrl() arguments > 3, last argument give number of pfield
// score instructions, schedule etc. must take into account it
 
instr 1
k4 = ctrl(4)
k5 = ctrl(5)
endin 
schedule(1,0,0,0,0)

instr 2
asig = oscil(ctrl(5), ctrl(4), 2)
outs(asig, asig) 
endin



i 2.01 0 1 60 0.1 
e

 

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Pass by reference should be preferred in general as it is more efficient. So if this code is working now for you, it's better than old-style.
We just need to treat input and output with more care

1- use input arguments as read-only unless you are explicitly looking to do in-place computation or some other particular side-effect.

2- only pass to output local variables created inside the UDO. There should not be a reason to do any different.

So, for rule 1, avoid

opcode op(var:i):i
var += 1
...


unless you want the side effect of incrementing the input.

For rule 2, this

opcode op(var:i):i
...
xout(var)
endop

should be avoided as it may lead to confusion.
In your earlier example, the global var was also causing an issue I think. Instead, this is the correct way

opcode op(var:i):i
lvar:i = var
...
xout(lvar)
endop

With a little bit of care, it should all work well.

Prof. Victor Lazzarini
Maynooth University
Ireland

> On 26 Apr 2026, at 08:50, Jean Basile Sosa  wrote:
>
> Hi Victor,
>
> I think I now understand the main difference between the two style approaches, and more generally advantages and limits of the pass by reference concept. Thank you.
>
> The following code works well, but I'm never completely sure of the relevance and the good way in Csound...
> After a quick look nothing lets consider future bugs?
>
> 
> 
> -odac
> 
> 
>
> sr = 44100
> ksmps = 128
> nchnls = 2
> 0dbfs  = 1
>
> gisquare ftgen 2, 0, 16384, 10, 1, 0 , .33, 0, .2 , 0, .14, 0 , .11, 0, .09
>
> opcode ctrl(pfield:i):(k)
> chnidx:S = sprintf("%.02f_p%d", p1, pfield)
> fieldvalue:i = pindex(pfield)
> print(fieldvalue)
> chnset(fieldvalue,chnidx)
> value:k init fieldvalue
> value:k = chnget(chnidx)
> puts(chnidx, 1)
> xout(value)
> endop
>
> // ctrl() arguments > 3, last argument give number of pfield
> // score instructions, schedule etc. must take into account it
>
> instr 1
> k4 = ctrl(4)
> k5 = ctrl(5)
> endin
> schedule(1,0,0,0,0)
>
> instr 2
> asig = oscil(ctrl(5), ctrl(4), 2)
> outs(asig, asig)
> endin
>
> 
> 
> i 2.01 0 1 60 0.1
> e
> 
> 
>
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