@array[0] and $array[0] are very similar. In fact, in scalar context, they evaluate to the same thing. warnings aside, there are two differences between slices and indexed elements. First, the index expression for the slice is evaluated in list context while the index expression for the element is evaluated in scalar context. Second, the slice creates a list context when used as an lvalue while the element creates a scalar context.

Thanks for the tip. But I still don't understand why
print @{@{$hash{"one"}}[0]}, "\n";
does not generate a warning instructing me to use
print @{${$hash{"one"}}[0]}, "\n";
while

my @array = (4,5,6);
print @array[0];
[download]

generates a warning instructing me to use $array[0].
Anyone? Thanks a lot in advance

For the same reason that this also issues the warning:

@array = qw[ foo bar qux ];;
print @{ array }[ 0 ];;
Scalar value @{ array }[ 0 ] better written as ${ array }[ 0 ] at 
foo
[download]

But these do not:

$name = 'array';;
print @{ $name }[ 0 ];;
foo

$ref = \@array;;
print @{ $ref }[ 0 ];;
foo
[download]

As this scrunched up deparse output shows, the extra level of indirection means that the code goes through a different path, and the warning has never been attached to that other path:

9  <;> nextstate(...)v ->a    9 <;> nextstate(...) v ->a         
g  <@> print vK ->h           g <@> print vK ->h
a   <0> pushmark s ->b        a  <0> pushmark s ->b
f   <@> aslice lK ->g         f  <@> aslice lK ->g
b    <0> pushmark s ->c       b   <0> pushmark s ->c
c    <$> const[IV 0] s ->d    c   <$> const[IV 0] s ->d
e    <1> rv2av[t5] sKR/1 ->f  e   <1> rv2av[t4] sKR/1 ->f
d     <#> gv[*array] s ->e    -    <@> scope sK ->e
-e syntax OK                  -     <0> ex-nextstate v ->d
                              d     <$> const[PV "array"] s ->e
                              -e syntax OK
[download]

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