update just tried mr robot's solution and found, to my surprise, that the double curlies aren't required. I would have expected

Actually, you missed a comma that impossiblerobot's code contained. His code was:

my @record = map { bytes => $_ }, get_bytes($num);

and that comma between the arguments to map makes map interpret the first argument as an EXPR not a BLOCK.

BTW, my perl (5.6.1) chokes on the code in your update:

perl -e '@a = map {k => $_} (1..3)'
syntax error at -e line 1, near "}("
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-sauoq
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