Why does a single number fail to match a Range object in an array?

When the regex engine sees /@numbers/ it treats that like an alternation of the array elements, so your first two examples are equivalent.

There just is no such automatism for Ranges I believe.

Edit: Never mind below, I totally misread the question at first.

> my @ranges = 1..3, 4..6;
[1..3 4..6]
> 1 ~~ @ranges[0];
True
> 2 ~~ @ranges[1];
False
> 4 ~~ @ranges[1];
True
> @ranges.first( 5 ~~ * )
4..6

See? @ranges is a array of, well, ranges (your call to item does nothing here). Theoretically this would hold true if the smartmatch operator were smarter.

> 1..3 ~~ @ranges;
False

Flattening also doesn't help, because a flat list of ranges is still a list of ranges.

Flattening the ranges themselves is possible, but that simply turns them into Arrays

> my @ranges2 = |(1..3), |(4..6)
[1 2 3 4 5 6]

Why does single number fails to match Range object in array?

Per the doc:

The interpolation rules for individual elements [of an array] are the same as for scalars

And per the same doc section the rule for a scalar (that is not a regex) is:

interpolate the stringified value

A range object such as 1..3 stringifies to 1 2 3:

my $range = 1..3;
put $range;                   # 1 2 3
put so '1'     ~~ / $range /; # False
put so '1 2 3' ~~ / $range /; # True

So, as Holli suggests, perhaps instead:

my @ranges = flat 1..3, 4..6;
say @ranges;        # [1 2 3 4 5 6]
say 1 ~~ /@ranges/; # ｢1｣

Or is there some reason you don't want that? (See also Scimon's comment on Holli's answer.)