| Newbie questions about Pliant
clearing an array
array to be returned is not cleared. |
| Message posted by maybe Boris Reitman on 2007/01/20 23:32:01 |
The function below clears item_list array properly only if I uncomment
item_list size := 0. Otherwise, the caller of this function gets a
return value that is polluted from a previous call to the function.
function catalog_search query -> item_list
arg Str query
arg Array:Str item_list
item_list := (var Array:Str empty)
#item_list size := 0
var List:Str tokens := lower:query hungry_split " "
each record flower_database:data
if (match_item_codes query keyof:record)
console "HERE" eol
item_list += keyof:record
else
var FlowernetItem fnitem
fnitem init "ftd" keyof:record
var Str f_title := lower fnitem:get_title
each token tokens
if token <> "" and (f_title search token -1) <> -1
console "THERE: " token eol
item_list += keyof:record
The caller code:
function test
var Array:Str items := catalog_search "orchid"
ok items:size > 1
is get_title:(items:0) "Lavender Phalaenopsis Orchid"
for (var Int count) 0 items:size-1
console "Got " items:count eol
var Str code := items:0
var Array:Str items2 := catalog_search code
is items2:size 1
is get_title:(items2:0) "Lavender Phalaenopsis Orchid"
for (var Int count) 0 items2:size-1
console "Got' " items2:count eol
The output:
1..25
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
ok
ok
Got C34-3579
Got Intercat-1711
Got Intercat-2001
Got Intercat-2225
Got Intercat-2408
Got Intercat-2604
Got Intercat-3006
Got Intercat-3407
Got Intercat-3716
Got Intercat-4848
Got W10-3354
Got W8-3862
Got WG916
HERE
not ok
#expected 1 but got 14
ok
Got' C34-3579
Got' Intercat-1711
Got' Intercat-2001
Got' Intercat-2225
Got' Intercat-2408
Got' Intercat-2604
Got' Intercat-3006
Got' Intercat-3407
Got' Intercat-3716
Got' Intercat-4848
Got' W10-3354
Got' W8-3862
Got' WG916
Got' C34-3579
If I uncomment the line: item_list size := 0, then this is the output:
1..25
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
THERE: orchid
ok
ok
Got C34-3579
Got Intercat-1711
Got Intercat-2001
Got Intercat-2225
Got Intercat-2408
Got Intercat-2604
Got Intercat-3006
Got Intercat-3407
Got Intercat-3716
Got Intercat-4848
Got W10-3354
Got W8-3862
Got WG916
HERE
ok
ok
Got' C34-3579
As you see, in the correct version I have only one "Got'" line.
It seems that the line "item_list size := 0" triggers the initialization mechanism,
because even if I just query the value of "item_list:size" like this,
console items_list:size eol
it works too.
Thanks,
Boris |
| Message posted by maybe Hubert Tonneau on 2007/01/21 02:11:38 |
This is a bug with the Pliant code generator optimiser.
One of the features of the Pliant code optimiser is to try to avoid copying
as much as possible through sharing the variables.
As an example, if you have:
d := a+b+c
the compiler produces:
t1 := a+b
t2 := t1+c
d := t2
where 't1' and 't2' are temporary variables,
and the code optimiser tries to share 't2' with 'd' in order to save one copy.
So, when you write
item_list := var Array:Str empty
Pliant code generator just incorrectly assumed that it could share 'item_list'
and 'empty'
When you write
item_list size := 0
no wrong optimisation is possible,
and just adding a 'console' in your function may also prevent the wrong
optimisation because one of the variable will be used at a new place adding
some contrains that can prevent the optimisation to be wrongly concluded as
possible.
The bad news is that correcting such a bug can take a very long time because
fixing a code generator optimiser is a nightmare. |