Re^8: Passing argument by reference (for a scalar)(Unary Plus)

> 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}

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Re^9: Passing argument by reference (for a scalar)(Unary Plus) by choroba (Cardinal) on Sep 11, 2024 at 11:35 UTC
Which, in turn, sometimes needs another similar trick: `my %hash = map { "a$_" => undef } @list; # syntax error at ... line +1, near "} @list" my %hash = map {; "a$_" => undef } @list; # OK.` [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^10: Passing argument by reference (for a scalar)(Unary Plus) by LanX (Saint) on Sep 11, 2024 at 15:13 UTC
Granted, in this case you are right. ++ And I hate this ambiguity, because the parser can't defer parsing the inside of the block till it sees if a comma is following or not `} , @list` is hash `} @list` is block Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^9: Passing argument by reference (for a scalar)(Unary Plus) by etj (Priest) on Sep 11, 2024 at 14:38 UTC
The "usual notation" you cite has the disadvantage that it has to create, then destroy, a scope for each element of `@list`, which is an unnecessary performance hit.	[reply] [d/l]
Re^10: Passing argument by reference (for a scalar)(Unary Plus) by LanX (Saint) on Sep 11, 2024 at 15:00 UTC
Well those performance hits are often marginal. I'd be interested to see a benchmark justifying the disadvantages of higher reading entropy and confused co-maintainers. Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply]