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In terms of the relative speeds, running the code through B::Concise is maybe helpful.

I can't interpret the full details, but the code to return a list of keys has fewer operations and only one nextstate (so less bookkeeping?). Both have the same number of ops that are optimised away (those preceded by "ex-").

Hopefully someone with better knowledge of the internals and B::Concise can shed some light.

C:\path>perl -v | find "This is" This is perl 5, version 28, subversion 0 (v5.28.0) built for MSWin32-x +64-multi-thread
C:\path>type return_hash_keys.pl use strict; use warnings; sub zort { my %hash = (a => 1); return keys %hash; }; my @x = zort(); #my $aa = $x[0]; C:\path>perl -MO=Concise,-src return_hash_keys.pl a <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 # 7: my @x = zort(); 2 <;> nextstate(main 6 return_hash_keys.pl:7) v:*,&,{,x*,x&,x$,$ - +>3 9 <2> aassign[t2] vKS/COM_AGG ->a - <1> ex-list lK ->7 3 <0> pushmark s ->4 6 <1> entersub lKS/STRICT ->7 - <1> ex-list lK ->6 4 <0> pushmark s ->5 - <1> ex-rv2cv sK/STRICT,1 ->- 5 <#> gv[IV \&main::zort] s ->6 - <1> ex-list lK ->9 7 <0> pushmark s ->8 8 <0> padav[@x:6,7] lRM*/LVINTRO ->9 return_hash_keys.pl syntax OK
C:\path>type return_hash_ref.pl use strict; use warnings; sub zort { my %hash = (a => 1); return \%hash }; my $x = zort(); my @x = keys %$x; #my $aa = $x[0]; C:\path>perl -MO=Concise,-src return_hash_ref.pl g <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 # 7: my $x = zort(); 2 <;> nextstate(main 6 return_hash_ref.pl:7) v:*,&,{,x*,x&,x$,$ -> +3 7 <2> sassign vKS/2 ->8 5 <1> entersub sKS/STRICT ->6 - <1> ex-list sK ->5 3 <0> pushmark s ->4 - <1> ex-rv2cv sK/STRICT,1 ->- 4 <#> gv[IV \&main::zort] s ->5 6 <0> padsv[$x:6,8] sRM*/LVINTRO ->7 # 8: my @x = keys %$x; 8 <;> nextstate(main 7 return_hash_ref.pl:8) v:*,&,{,x*,x&,x$,$ -> +9 f <2> aassign[t6] vKS/COM_AGG ->g - <1> ex-list lK ->d 9 <0> pushmark s ->a c <1> keys[t5] lK/1 ->d b <1> rv2hv[t2] lKRM/STRICT ->c a <0> padsv[$x:6,8] sM/DREFHV ->b - <1> ex-list lK ->f d <0> pushmark s ->e e <0> padav[@x:7,8] lRM*/LVINTRO ->f return_hash_ref.pl syntax OK

In reply to Re^6: Using 'keys' on a list by swl
in thread Using 'keys' on a list by lammey

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