Perl: Return hashref from function does not work

Question

I was fooling around with some obfuscated code that doesn't do anything useful when I encountered some strange behaviour I did not understand.

Here's my code.

no strict;
sub foo{1&&{${$_[0]},${$_[0]}}}say map {&${${_}}(${_})->{${${_}}}}map{\$_}qw(foo);

And in indented:

no strict;
sub foo {
  1 && { ${$_[0]} => ${$_[0]} }
}
say map { &${ ${_} }( ${_} )->{ ${ ${_} } } }
  map { \$_ } qw (foo);

What it should do is take the string foo , build a reference to it, and then call the function with that name ( &foo ). That function should return a hashref where both key and value are said foo string. After that, it prints the value of the returned hashref's key foo , which is foo .

So far, so good. Not useful, but still fun. The strange thing is, when I remove the 1 && part in the sub, it returns a list despite the curlies, and I have no clue why it does that.

If I just say sub foo { { 'foo'=>'foo' } } it returns the reference. Why doesn't it in my case? And furthermore, why does it when I add 1 && ?

Answer 1

Without the 1 && part the curly braces are interpreted as a block thus returning a list. With the additional part the perl interpreter makes an anonymous hashreference as desired.

Instead of the 1 && you could also use a simple + to help the perl interpreter:

sub foo {
  +{ ${$_[0]} => ${$_[0]} }
}