Question about rules for autovivification

Hi,

Im trying to figure out an aspect of the autovivification. Specifically why
the construct being used changes whether autovivification occurs or not. Ie
for the deref @{EXPR}, whether autovivification occurs is dependent on both
the type of EXPR and the context within which @{EXPR} is used.

For instance 

  D:\>perl -Mstrict -wle "my $f = { }; my @a=map { $_ } @{ $f->{foo} }"

  D:\>perl -Mstrict -wle "my $f = { }; print 'ok' for @{ $f->{foo} }"

  D:\>perl -Mstrict -wle "my $f = { }; my @a=@{ $f->{foo} }"
  Can't use an undefined value as an ARRAY reference at -e line 1.

  D:\>perl -Mstrict -wle "my $f = { }; print 'ok' if @{ $f->{foo} }"
  Can't use an undefined value as an ARRAY reference at -e line 1.

  D:\>perl -Mstrict -wle "my $f = { }; print 'ok' for @{ undef() }"
  Can't use an undefined value as an ARRAY reference at -e line 1.

Now im well aware that @{EXPR} autovivifies when its directly or indirectly
used as STORE, ie:

  D:\>perl -Mstrict -wle "my $f = { }; push @{ $f->{foo} },'foo'"

But why does it autovivify in a FETCH here:

  D:\>perl -Mstrict -wle "my $f = { }; pop @{ $f->{foo} }"

but not here

  D:\>perl -Mstrict -wle "my $f = { }; print 'ok' if @{ $f->{foo} }"
  Can't use an undefined value as an ARRAY reference at -e line 1.

Any wisdom regarding this would be welcome.

Yves

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