From @dogbert17

dogbert@​dogbert-VirtualBox ~/.rakudobrew/moar-nom $ perl6 -v
This is Rakudo version 2016.07.1-128-g715b822 built on MoarVM version 2016.07-16-g85b6537
implementing Perl 6.c.

dogbert@​dogbert-VirtualBox ~/.rakudobrew/moar-nom $ perl6 -e 'say (1,2,3).invert'
Method 'value' not found for invocant of class 'Int'
  in block <unit> at -e line 1

http://irclog.perlgeek.de/perl6/2016-08-06

12​:58​:01 dogbert17 | m​: say (1,2,3).invert # ??
12​:58​:01 +camelia | rakudo-moar 589061​: OUTPUT«Method 'value' not found for invocant of class 'Int'␤ in block <unit> at <tmp> line 1␤␤»
12​:59​:18 lizmat | dogbert17​: all I can say is that TimToady added/changed it early 2015

...

13​:16​:34 lizmat | apparently you can only List.invert if the List contains pairs
13​:18​:13 lizmat | dogbert17​: so In guess the right course of action would be to rakudobug it as a @​LARRY bug
13​:20​:02 dogbert17 | lizmat​: so the bug is that it only handles list of pairs?
13​:21​:02 lizmat | well, I guess the bug is that the error is really LTA if the list does not consist of pairs *OR* it should call .pairs on itself first before inverting
13​:21​:13 lizmat | (aka, be the same as .antipairs)

From @zoffixznet

My vote is to not have .invert on listy things at all.

The fact that it can't work in some cases, depending on what things a list contains, is a good indication to me that it's not a list method.

The second option for me would be to improve the error message and make it work only on lists with just Pairs in them, so
that .invert on (1, 2, 3).pairs (which returns a Seq of Pairs) can be used without surprises of .pairs called again under the hood.

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

From @TimToady

Binding of the map routine internally now requires list elements to bind as Pair, which improves the error message.

(The alternate approach of inserting a CATCH into the map closure could in theory produce an even better message, but it appeared to slow things down more than the Pair binding approach.)

Note that we cannot make the degenerate case of .invert the same as .antipairs, because .invert must expand list values into multiple antipairs. In any case, .antipairs is 5-10 times faster since it doesn't have to check for such expansion.

Fix in baeabb4c4e8f5d223da8632130b4dfcd020d40ba

Test in 63c1f009b910a5c87186b2201383682ad7a0f724

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