OpenEuphoria

1. sequence question

• Posted by Tone Škoda <tskoda at email.si> Sep 04, 2004
• 510 views

sequence s1, s2
s1 = repeat (0, 1000000) -- s1 is 3.8MB big
s2 = {{}}
s2 [1] = s1

will this last line of code:
1. make copy of s1 into s2 [1]
2. or will it only make pointer to s1?

similar is this:
s2 = {repeat (0, 1000000)}
s1 = s2 [1] -- what happens here?

if it is number 1 then it is waste of memory.
in cases like this i like C more because it is more clear what happens.

i'm asking this because i want to create a library which is not specific for
program. and in this library one sequence1 appears in many different sequences. i
could only have one copy of this sequence1, not many same copies which would
exist in these different sequences. here pointers would be nice.

i would like pointers and structures added to euphoria.
pointers are good because you can identify a variable without having to copy it
in memory. you can do that in euphoria but it's much more complicated. structures
are also possible in euphoria but again not on simple easy way. and structures
are needed in every program.

3. Re: sequence question

• Posted by Derek Parnell <ddparnell at bigpond.com> Sep 04, 2004
• 483 views

Tone Škoda wrote:
> 
> sequence s1, s2
> s1 = repeat (0, 1000000) -- s1 is 3.8MB big
> s2 = {{}}
> s2 [1] = s1
> 
> will this last line of code:
> 1. make copy of s1 into s2 [1]
> 2. or will it only make pointer to s1?
> 
> similar is this:
> s2 = {repeat (0, 1000000)}
> s1 = s2 [1] -- what happens here?
> 
> if it is number 1 then it is waste of memory.
> in cases like this i like C more because it is more clear what happens.

I think, and I stress *think*, what happens is that the 'copied' sequence
is just a pointer to the original until such time as the original 
is changed, then you get a real copy done. All of this happens in the
background.

 sequence s1, s2
 s1 = repeat (0, 1000000) -- s1 is 3.8MB big
 s2 = {{}}
 s2 [1] = s1  -- s2[1] now points to s1.
 s1[1] = 1 -- This also triggers a copy of the original s1
            -- so that s2[1] now contains (points to actually) a
            -- copy of s1.


> i'm asking this because i want to create a library which is not specific for
> program.
> and in this library one sequence1 appears in many different sequences. i could
> only
> have one copy of this sequence1, not many same copies which would exist in
> these different
> sequences. here pointers would be nice.
> 
> i would like pointers and structures added to euphoria.
> pointers are good because you can identify a variable without having to copy
> it in
> memory. you can do that in euphoria but it's much more complicated. structures
> are
> also possible in euphoria but again not on simple easy way. and structures are
> needed
> in every program.

The way that I do things so it has the same effect as pointers is that 
I have a 'global' sequence and pass a 'pointer' to it in the form of an
index.

eg.

global sequence PH PH = {}
sequence PHalloced PHalloced = {}

global function allocPH()
   integer lPos
   lPos = find(0, PHalloced)
   if lPos then
       PHalloced[lPos] = 1
       return lPos
   end if

   PH &= 0
   PHalloced &= 1
   return length(PHalloced)
end function

global procedure freePH(integer pPos)
   if pPos > 0 and pPos <= length(PH) then
        PH[pPos]=0
        PHalloced[pPos] = 0
   end if
end procedure

global function isAllocedPH(integer pPos)
   if pPos > 0 and pPos <= length(PH) then
        return (PHalloced[pPos] != 0)
   else
        return -1
   end if
end function

integer x
sequence s1,s2
x = allocPH()
PH[x] = repeat(0, 1000000)

s1 = {x} -- points to sequence
s2 = {x} -- points to sequence.

PH[ s1[1] ][1] = 1  -- assign using S1
? PH[ s2[1] ][1]    -- read using S1

freePH(x)
if isAllocedPH(x) then
    ? PH[s2[1]][1]
else
    ? 3
end if

So in short, Heap based objects can be passed by reference using this
technique.

And yes, datatype-safe structures would be nice because the Euphoria
would validate the datatype-ness rather than leaving it up to the
programmer.

-- 
Derek Parnell
Melbourne, Australia

5. Re: sequence question

• Posted by LEVIATHAN <leviathan at uswest.net> Feb 02, 2001
• 513 views
• Last edited Feb 03, 2001

> Ok, why can't i do this:
> 
> Syntax error - expected to see possibly 'end', not '['
>    theword[loop] = {'e','e','e','e','e','E','E','E','E'}[loop]

I assume you can't add [#] to the end of a sequence. But it doesn't 
make sense to me... the one below makes more sense, Kat...

> array = {'e','e','e','e','e','E','E','E','E'}
> theword[loop] = array[loop]
> 
> it's ok.

Yeah, makes sense, makes sense... {} isn't considered a 
procedure, perhaps?

--"LEVIATHAN"