From type/Metamodel/MultipleInheritance

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method add_parent($obj, $parent, :$hides)

Adds $parent as a parent type. If $hides is set to a true value, the parent type is added as a hidden parent.

$parent must be a fully composed typed. Otherwise an exception of type X::Inheritance::NotComposed is thrown.

From type/Metamodel/EnumHOW

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method add_parent($obj, $parent)

Sets the base type of an enum. This can only be used if no base type was passed to .new_type.