Course of Raku / Advanced / Introspection with MOP

WHAT and ^name

WHAT is a pseudo-method that gives access to information about the type of the variable.

You can use it in the same way you use ^name:

my $var = 42;

say $var.^name;
say $var.WHAT;

The program prints the type of the value with some minor decoration differencies:

Int
(Int)

Notice that for a variable without type constraints, the default type is Any. As soon as you assign a value, the type returned by ^name and WHAT changes:

my $var;
say $var.^name; # Any
say $var.WHAT;  # (Any)

$var = 'Hello';
say $var.^name; # Str
say $var.WHAT;  # (Str)

With a type constrait, the type of the contents of the container is known immediately after creation:

my Str $var;
say $var.^name; # Str
say $var.WHAT;  # (Str)

$var = 'Hello';
say $var.^name; # Str
say $var.WHAT;  # (Str)