$a $b Type of Match Implied Matching Code
====== ===== ===================== =============
Any undef undefined !defined $a
Any Object invokes ~~ overloading on $object, or dies
Hash CodeRef sub truth for each key[1] !grep { !$b->($_) } keys %$a
Array CodeRef sub truth for each elt[1] !grep { !$b->($_) } @$a
Any CodeRef scalar sub truth $b->($a)
Hash Hash hash keys identical (every key is found in both hashes)
Array Hash hash slice existence grep { exists $b->{$_} } @$a
Regex Hash hash key grep grep /$a/, keys %$b
undef Hash always false (undef can't be a key)
Any Hash hash entry existence exists $b->{$a}
Hash Array hash slice existence grep { exists $a->{$_} } @$b
Array Array arrays are comparable[2]
Regex Array array grep grep /$a/, @$b
undef Array array contains undef grep !defined, @$b
Any Array match against an array element[3]
grep $a ~~ $_, @$b
Hash Regex hash key grep grep /$b/, keys %$a
Array Regex array grep grep /$b/, @$a
Any Regex pattern match $a =~ /$b/
Object Any invokes ~~ overloading on $object, or falls back:
Any Num numeric equality $a == $b
Num numish[4] numeric equality $a == $b
undef Any undefined !defined($b)
Any Any string equality $a eq $b
1 - empty hashes or arrays will match.
2 - that is, each element smart-matches the element of same index in the
other array. [3]
3 - If a circular reference is found, we fall back to referential equality.
4 - either a real number, or a string that looks like a number