> 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

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]

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}

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.

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}