Exception thrown when trying to assign to something read-only
class X::Assignment::RO is Exception {}
Code like
sub f() { 42 };
f() = 'new value'; # throws an X::Assignment::RO
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Assignment::RO: Cannot modify an immutable Any»
throws an exception of type X::Assignment::RO.
method typename(X::Assignment::RO:D: --> Str)
Returns the type name of the value on the left-hand side