Re: [Gretl-devel] members of lists returned from functions
Am 10.02.2008 17:04, Allin Cottrell schrieb:
On Sat, 9 Feb 2008, Sven Schreiber wrote:
> The example script below prints two identical series under the
> name of "s1", which is "obviously" wrong...
Ah, there's a loose end here, in terms of behavior when a function
returns a list: what should happen if the list contains
one or more variables that have the same name as a variable that
already exists at the caller level?
What's happening at present can be exposed by this variant on
Sven's script:
function test(void)
series s1 = randgen(u,0,1)
series s2 = randgen(u,2,3)
list myl = s1 s2
print "in test"
print s1 -o
return list myl
end function
nulldata 4
loop 2
list check = test()
varlist
print "in caller"
print s1 -o
end loop
The last "varlist" produces:
Listing 6 variables:
0) const 1) index 2) s1 3) s2 4) s1
5) s2
which is not nice. It seems to me the second iteration should
overwrite s1 and s2 -- agreed?
At first I thought "yes" (and it was what I was proposing originally),
but then it occurred to me that the fact that returning lists from
functions would affect the caller's namespaces is a "policy breach".
Because in theory it's possible that at the caller level there exists a
series of the same name just by coincidence, which would then get
deleted. So before you could use a function written by somebody else you
would have to study it and make sure it doesn't have this side effect.
IMHO that's bad.
Ok, so the probability of this problem occurring in practice may be
minimal, and so feel free to discard this objection.
But without having thought too much about it, let me just give an
example of how it could perhaps work:
Suppose that "list indexing" is introduced as a new syntax; that would
mean that in the above example you could access the series within the
list 'check' by a one-dimensional index: check[1], check[2] etc. up to
check[nelem(check)]. (And you would not be able to use the names 's1' or
's2' at the caller level, they would be restricted to the
scope/namespace of the function.) However, I admit it's not 100% clear
how the series would be displayed in the GUI without running into the
namespace collision problem again.
just a thought,
sven