Re: keys on scalar warnings and lack thereof

See Mini-Tutorial: Dereferencing Syntax.

The curlies in a circumfix dereference can only be omitted if they contain a simple scalar like $NAME (or $BLOCK), not something more complicated like $_[0].

%$_[0] should be %{ $_[0] } (circumfix notation) or $_[0]->%* (postfix notation).

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Re^2: keys on scalar warnings and lack thereof by Anonymous Monk on May 14, 2026 at 18:07 UTC
I didn't include %{$_[0]} because it's obviously ok: perl -MDevel::Peek -e 'Dump(%{$_[0]})' SV = PVHV(0x157010280) at 0x15700ae40 REFCNT = 1 FLAGS = (SHAREKEYS) ARRAY = 0x0 KEYS = 0 FILL = 0 MAX = 7 But what is this: perl -MDevel::Peek -e 'Dump(%$_[0])' SV = NULL(0x0) at 0x100939eb8 REFCNT = 2147483641 FLAGS = (READONLY,PROTECT) and this: perl -MDevel::Peek -e 'Dump(%$^[0])' SV = IV(0x159825cf0) at 0x159825d00 REFCNT = 1 FLAGS = (PADTMP,IOK,pIOK) IV = 5796572328 perl -MDevel::Peek -e 'Dump(%{$^[0]})' Number found where operator expected (Missing operator before "0"?) [download] And all the other weird looking results?	[reply] [d/l]
Re^3: keys on scalar warnings and lack thereof by LanX (Saint) on May 14, 2026 at 18:35 UTC
What exactly do you expect from broken code? `$ perl -E' $_[0] = {}; say keys %$_[0]' Experimental keys on scalar is now forbidden at -e line 1. Type of arg 1 to keys must be hash or array (not index/value array sli +ce) at -e line 1, at EOF Execution of -e aborted due to compilation errors.` [download] Please note the not index/value array slice , because that's what's fed into keys. Try `keys %{$_}[0]` and compare the error messages... Update Admittedly, I've never used this before: Index/Value-Array-Slices Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply] [d/l] [select]

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