I'm still waiting for someone to understand my question...

I understand it (I think) :-) The difference between map { $_++ } 1 failing and map { $_++ } [] not failing, or even map { $_++ } \1 not failing, is pretty clear to me. I just don't have an answer for you :-(

With [], I understand the arguments that it's a constructor, for example sub foo () { 1 } can be inlined, but sub bar () { [] } returns a new anonymous array each time. But something like map { $_++ } \undef or map { $_=3 } \1 not failing doesn't entirely make sense to me yet (note map { $$_++ } \undef does fail).

As an aside, I was playing around in the console a bit and can't yet wrap my head around this, it feels buggy, but that may just be because it's getting late here:

$ perl -wMstrict -MData::Dump -e 'dd $_ for map { $_++ } \undef'
\undef
$ perl -wMstrict -MData::Dump -e 'dd $_ for map { ++$_ } \undef'
94067726450329
[download]

Update: Nevermind, it clicked, d'oh. Also made a few minor edits to the above. Update 2: Oops, looks like my update came at just about the same time as your reply, sorry.