Impossible. You're asking to do something that's the very definition of looping without using a loop. What do you actually want? 

my $val = Dive(\%b, map \$_, @a);
DiveVal(\%b, map \$_, @a)= $val;

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Check out Data::Diver. 

my $val = Dive(\%b, map \$_, @a);
DiveVal(\%b, map \$_, @a) = $val;

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If @a contains no numbers, you can omit map \$_,. 

my $val = Dive(\%b, @a);
DiveVal(\%b, @a) = $val;

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Update: I thought you had $b{$a[0], $a[1], $a[2]}. Using a slice is definitely the cleanest solution. You'd still be looping, though.

In reply to Re: use array for hash-keys without loop by ikegami
in thread use array for hash-keys without loop by piccard

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