What's the deal with all the different Perl 6 equality operators? (==, ===, eq, eqv, ~~, =:=, …)

Question

Perl 6 seems to have an explosion of equality operators. What is =:=? What\'s the difference between leg and cmp? Or eqv and

Answer 1

=:= tests if two containers (variables or items of arrays or hashes) are aliased, ie if one changes, does the other change as well?

my $x;
my @a = 1, 2, 3;
# $x =:= @a[0] is false
$x := @a[0];
# now $x == 1, and $x =:= @a[0] is true
$x = 4;
# now @a is 4, 2, 3 

As for the others: === tests if two references point to the same object, and eqv tests if two things are structurally equivalent. So [1, 2, 3] === [1, 2, 3] will be false (not the same array), but [1, 2, 3] eqv [1, 2, 3] will be true (same structure).

leg compares strings like Perl 5's cmp, while Perl 6's cmp is smarter and will compare numbers like <=> and strings like leg.

13 leg 4   # -1, because 1 is smaller than 4, and leg converts to string
13 cmp 4   # +1, because both are numbers, so use numeric comparison.

Finally ~~ is the "smart match", it answers the question "does $x match $y". If $y is a type, it's type check. If $y is a regex, it's regex match - and so on.