Thanks!

That's why I prefer

${ shift() }

even if it needs one letter more.

+ is the unary-+ operator. It does absolutely nothing but evaluate to the same thing its operand does. It even provides the same context as the one in which it's evaluated.

+5        # Same as `5`
+"abc"    # Same as `"abc"`
+@a       # Same as `@a`, in both scalar and list context
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${ shift } is just a weird undocumented way of writing $shift. I didn't want that. I wanted to use the shift operator. ${ +shift } can't be parsed as a scalar named +shift, so it has the desired effect.

It's not undocumented: https://perldoc.perl.org/perldata#Demarcated-variable-names-using-braces

It's documented to be allowed in string literals, but the OP is not using it in a string literal.

A truly useful use of + is for constructing hashes with map:

my %hash = map +($_=>undef), @list;
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Without the +, Perl would think you wanted to call map with 2 args, not over @list.

> A truly useful use of + is for constructing hashes with map:

> my %hash = map +($_=>undef), @list;

For varying definitions of "useful". This needs 2 letters more than the usual notation

my %hash = map {$_=>undef} @list; °

update

°) see choroba's reply why the parser will have trouble interpreting this.

FWIW: I'd use a hash-slice @hash{@list} = () anyway

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}