Unexpected flattening of arrays when initalizing an array

Question

I'm not totally sure if this is a bug, a quirk, or simply a bad practice, but this is what happens:

[0] > my @nope = [["a","b"]]; @nope.push: ["b","c"]
[a b [b c]]
[1] > my @yipee = []; @yipee.push: [["a","b"]]; @yipee.push: ["b","c"]
[[a b] [b c]]

So if you inialize an array with a list of lists, it gets Slipped, forcing to use 2 steps to initalize it. Is there something I'm missing here?

In the first example does the outer set of square brackets essentially 'de-containerize' the inner bracket? So that when you push ["b","c"] you get [a b [b c]] ? — jubilatious1
– jubilatious1, Commented Oct 16, 2024 at 10:03

Elizabeth Mattijsen · Accepted Answer · 2024-10-16 09:14:51Z

5

Note that for the initialization of arrays, you don't need the outer pair of []. So your first example can be written as:

my @nope = ["a","b"];

Which may make the issue clearer to you: it's the single argument rule at work (which BTW allows you to say for @a { }). So either you need to make it look like more arguments by adding a comma (which makes it a List):

my @a = ["a","b"],;
dd @a;  # [["a", "b"],]

or you need to itemize the first array (as items never get implicitely flattened):

my @b = $["a","b"];
dd @b;  # [["a", "b"],]

answered Oct 16, 2024 at 9:14

Elizabeth Mattijsen

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2 Comments

jjmerelo Over a year ago

If I understood this directly, double square brackets are, in this context, understood as single square brackets. A case of not DWIM, maybe?

Elizabeth Mattijsen Over a year ago

You could use double square brackets, but you'd need to make the inner a List by adding a comma, so my @a = [["a", "b"],];. But really, the outer square brackets are superstitious :-)

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