[Gretl-devel] optional arguments (was Re: irf() and fevd())
Am 23.05.2018 um 19:45 schrieb Allin Cottrell:
On Wed, 23 May 2018, Sven Schreiber wrote:
> (Am I right in assuming that a new alpha argument could be added in
> the future without compromising backwards compatibility? What I mean
> is that a call like fevd(<int>, <bundle>) would still be possible if
> the in the future the signature would be: <int>, <optional-scalar>,
> <bundle>, right?)
Hmm, not really. You'd need an argument-separating comma, as in
fevd(<int>,,<bundle>)
It's true that since the (notional) second and third arguments here
are of different types, we could in principle check the types and
"see" that the argument given second must really be the third one, but
that sort of thing (auto-detection of implicitly omitted optional
arguments) is not supported in geneval.c for any functions at present.
Its also strikes me as kinda tricksy.
I found the part of the doc that inspired my hunch, it was in the
strsplit help:
<help-quote>
strings S = strsplit(basket,,",")
will split the input into an array of four strings using comma as
separator. The “extra” comma in the input above indicates that the i
argument is omitted, but it's not strictly necessary unless you wish to
extract a single element; if the second argument is a string and only
two arguments are given it is understood that sep rather than i is
intended. So
strings S = strsplit(basket, ",")
...
</help-quote>
So this only works in this particular function, not in general?
thanks,
sven