1:12 p.m.
Hi again,
so I've revisited the whole story about default function arguments. Some
time ago it was decided that for 'string' and 'matrix' types it is
possible to mark them as optional by appending '[null]', without using
pointers (which is still possible).
The same trick doesn't work for the array types 'strings' or
'matrices'
(or 'bundles', for that matter). Is there a specific reason?
To be clear, this does NOT work:
<hansl-fail>
function void ch2( strings ss[null])
if exists(ss)
print "exists"
elif !isnull(ss)
print "isn't null"
endif
end function
ch2()
</hansl-fail>
It would sometimes come in handy for optional array arguments.
thanks,
sven
7:49 p.m.
On Fri, 7 Apr 2017, Sven Schreiber wrote:
Hi again,
so I've revisited the whole story about default function arguments. Some time
ago it was decided that for 'string' and 'matrix' types it is possible to
mark them as optional by appending '[null]', without using pointers (which is
still possible).
The same trick doesn't work for the array types 'strings' or
'matrices' (or
'bundles', for that matter). Is there a specific reason?
That nobody has requested it to date?
To be clear, this does NOT work:
<hansl-fail>
function void ch2( strings ss[null])
if exists(ss)
print "exists"
elif !isnull(ss)
print "isn't null"
endif
end function
ch2()
</hansl-fail>
It would sometimes come in handy for optional array arguments.
Yes, except that the conditionality above is funny ;-) If x doesn't
exist, it's surely not going to be non-null!
OK, now (in git, not shapshots yet) I've enabled the "null" default
for all types that might reasonably be considered "pointery": so not
just arrays but also bundles and series.
If you (as a function writer) choose to give a "null" default for
any of these parameter types, you need to be ready to use exists()
to check whether the caller actually gave you anything.
As the caller of such a function you should be able to give "null"
(without the quotes), or just leave an empty argument slot, for
any arguments specified in this way.
Just to be clear, "null" is never acceptable -- either as a default
value when you're writing a function or as a dummy argument when
you're calling one -- for the scalar types (scalar, int, bool).
Allin
1:38 p.m.
Am 07.04.2017 um 21:49 schrieb Allin Cottrell:
If you (as a function writer) choose to give a "null"
default for any of
these parameter types, you need to be ready to use exists() to check
whether the caller actually gave you anything.
OK, except (reminder to self and perhaps to some others as well) if you
use the gretl list type. (Which is implicitly clear in your mention of
"these types", because you only spoke of arrays, bundles, series, not
lists.)
This example:
<hansl>
nulldata 10
function void cc(list in[null])
if !nelem(in)
if exists(in)
print "exists but empty"
endif
endif
end function
cc()
</hansl>
does print out "exists but empty" for me.
(BTW and completely different: $lang isn't syntax colored.)
thanks,
sven
2:49 p.m.
On Thu, 13 Apr 2017, Sven Schreiber wrote:
Am 07.04.2017 um 21:49 schrieb Allin Cottrell:
> If you (as a function writer) choose to give a "null" default for any of
> these parameter types, you need to be ready to use exists() to check
> whether the caller actually gave you anything.
OK, except (reminder to self and perhaps to some others as well) if you use
the gretl list type. (Which is implicitly clear in your mention of "these
types", because you only spoke of arrays, bundles, series, not lists.)
This example:
<hansl>
nulldata 10
function void cc(list in[null])
if !nelem(in)
if exists(in)
print "exists but empty"
endif
endif
end function
cc()
</hansl>
does print out "exists but empty" for me.
True, and I was aware of that. I decided to postpone discussion of the
point until after the 2017a release. It's awkward, and I'm not sure
exactly what to do about it. Maybe at this stage, with backward
compatibility in mind, we just have to document it plainly and admit
that it's an inconsistency.
(BTW and completely different: $lang isn't syntax colored.)
Now fixed in git.
Allin
2850
days inactive
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3 comments
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participants (2)
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Allin Cottrell -
Sven Schreiber