IMHO, there is an ever so subtle difference between navigation - using
the . operator explictly or implicitly (as with indexing) - and
arithmetic.
I am personally perfectly happy for my arithmetic expressions to fail
with any applicable exception if I throw unacceptable values at them.
H2
Den 2018-08-14 13:28, skrev ocs@ocs:
Gentlemen,
some NPE-related problems of today brought me to re-interate one of my
older suggestions.
We have the so-called “safe navigation”[*], which in some cases allows
a null to be propagated out of an expression instead of throwing a
NPE. At the moment, it can be triggered for a particular
sub-expression (like property/method-call and, as of 3, newly also
indexing) using a question mark (e.g., “foo?.bar()” or “foo?[bar]”).
Do please correct me if I am wrong, but far as I know, there still are
expressions which do not allow the “safe mode”, e.g., arithmetic
(“a+b” etc). Furthermore, there are cases when one simply wants a
bigger block of code to contain only null-propagating expressions and
never NPE; in such case, using the question mark syntax is both
inconvenient and error-prone (for it is very easy to forget one of the
lot of question marks needed in such a code, and then get an uncaught
unwanted NPE).
For these reasons, I would suggest adding a new annotation, whose name
might be e.g., “ImplicitSafeNavigation”; it would simply force a
null-propagation to be implicitly and automatically used for *all*
expressions in the annotated scope, i.e., NPE would never be thrown
for them; for example:
===
@ImplicitSafeNavigation class Foo {
static foo(a,b,c,d,e) {
a.bar+b*c[d]<<e.bax() // just e.g.; would work with *any*
expression which NPEs today
}
}
assert null == Foo.foo(null,null,null,null,null)
===
I wonder whether this enhancement would be possible to implement in
some forthcoming Groovy release? Myself, I believe it would help
tremendously.
If feasible, then it is for a further discussion whether in the scope
of this annotation
(a) a safe-navigation syntax (“foo?.bar”) should be ignored as
superfluous;
(b) or, whether in this scope it should reverse the behaviour to
trigger an NPE anyway;
(c) or, whether it should be ignored as (a), and aside of that it
would be worth the effort (and technically possible) to add another
syntax to force NPE over a particular sub-expression (e.g.,
“foo!.bar”).
Thanks and all the best,
OC
[*] The name might not be quite apt, for propagating a null is not
inherently safer than NPEing; those are simply two different
approaches, both of which serve best in different circumstances. A
better name would be something like “null-propagating” or “non-NPE”
mode, I guess. Myself, I don't think we should change the name though,
for all are used to it.
