error message mentions $a parameter of op signature: ++.++

[p6rt]

Migrated from rt.perl.org#126220 (status was 'resolved')

Searchable as RT126220$

[p6rt]

From @AlexDaniel

Code​:
++.++

Result​:
Parameter '$a' expected a writable container, but got Int value
  in block <unit> at ./test2.pl​:2

There is no $a in user code, so it should not be mentioned.

“$a” is mentioned because​:
.say for &postfix​:<++>.candidates

Result​:
sub postfix​:<++> (Mu​:D $a is rw) { #`(Sub|169376128) ... }
sub postfix​:<++> (Mu​:U $a is rw) { #`(Sub|169376224) ... }
sub postfix​:<++> (Bool​:U $a is rw) { #`(Sub|169375744) ... }
sub postfix​:<++> (Int​:D $a is rw) { #`(Sub|169375840) ... }
sub postfix​:<++> (int $a is rw) { #`(Sub|169375552) ... }
sub postfix​:<++> (Num​:D $a is rw) { #`(Sub|169375936) ... }
sub postfix​:<++> (Num​:U $a is rw) { #`(Sub|169376032) ... }
sub postfix​:<++> (num $a is rw) { #`(Sub|169375648) ... }

<FROGGS> AlexDaniel​: imagine you have a $a near that bit of code and waste
hours :o)

Indeed!

Same thing with -- and possibly other ops.

Perhaps there is some universal solution that will fix other problems like
this?

<jnthn> What is a bit bothersome is that we don't report that we're *in*
CORE.setting
<jnthn> So the backtrace makes it look like it could be in your own code
<FROGGS> jnthn​: don't we hide that information on purpose?
<jnthn> FROGGS​: Yeah, 'cus in other times it's annoying to do otherwise :P
<jnthn> Can't win! :)

[p6rt]

From @zoffixznet

The error is pretty good now. Perhaps, the ticket can be closed?

zoffix@​VirtualBox​:~$ perl6 -e '++.++'
Cannot resolve caller prefix​:<++>(Int); none of these signatures match​:
  (Mu​:D $a is rw)
  (Mu​:U $a is rw)
  (Int​:D $a is rw)
  (int $a is rw)
  (Bool $a is rw)
  (Num​:D $a is rw)
  (Num​:U $a is rw)
  (num $a is rw)
  in block <unit> at -e line 1

zoffix@​VirtualBox​:~$

[p6rt]

The RT System itself - Status changed from 'new' to 'open'

[p6rt]

From @AlexDaniel

On Sun Jun 19 16​:56​:55 2016, cpan@​zoffix.com wrote​:

The error is pretty good now. Perhaps, the ticket can be closed?

zoffix@​VirtualBox​:~$ perl6 -e '++.++'
Cannot resolve caller prefix​:<++>(Int); none of these signatures match​:
(Mu​:D $a is rw)
(Mu​:U $a is rw)
(Int​:D $a is rw)
(int $a is rw)
(Bool $a is rw)
(Num​:D $a is rw)
(Num​:U $a is rw)
(num $a is rw)
in block <unit> at -e line 1

zoffix@​VirtualBox​:~$

It looks like behavior changed before Christmas.

Perhaps a tests or two for ++.++ is not going to hurt?

[p6rt]

From @zoffixznet

Tests added in Raku/roast@4e973da24d

[p6rt]

@zoffixznet - Status changed from 'open' to 'resolved'