I wished I could up-vote you multiple times. :)

> but sub bar () { [] } returns a new anonymous array each time.

Interesting ... here a workaround

 
  DB<99> my $a =[]; sub bar () { $a }

  DB<100> sub tst { print bar,bar}

  DB<101> tst
ARRAY(0x3365bc0)ARRAY(0x3365bc0)
[download]

But sorry when I insist, the following case should be an error, because the aliased literal array will be destroyed afterwards, which sense does it make to alter it?

map { $_++ } []

I wouldn't mind map { $_+1 } [] tho.

> But something like map { $_++ } \undef not failing doesn't entirely make sense to me yet

agreed, I think it's simply not covered.

> As an aside, I was playing around in the console a bit and can't yet wrap my head around this,

... is pretty clear to me. I also have an answer for you ;-p

The first post -increment returns the original value before incrementing.

The second pre -increment returns the result, which is the numification of the reference +1

  DB<105> p []+1
53924433
[download]