Hello!
If roles are interfaces, do we want any class that provides an interface
consistent with a role to implicitly do the role? That is, if a class
fulfills all of the interface requirements of a role without actually
saying it does the role, does it do the role anyway?
role Documented {
has $.documentation;
}
class Foo does Documented { ... }
# I don't know why Bar isn't declared as doing Documented
# but it meets all the requirements of doing Documented...
class Bar {
has $.documentation;
}
my $baz = Foo.new( $documentation => "q to quit" );
my $qux = Bar.new( $documentation => "enter to continue" );
sub show_docs ( $obj.does( Documented ) ) { # or $obj ~~ Documented
say $obj.documentation;
}
show_docs( $baz ); # "q to quit"
show_docs( $qux ); # "enter to continue" -or-
# error because Bar doesn't explicitly do
# Documented?
I guess we don't really need implicit doing of roles to get both of
those objects to print their documentation, as we could have something like
sub show_docs ( $obj ) {
if ( defined $obj.documentation ) {
say $obj.documentation;
}
else {
die "Should have included a documentation string"
}
}
Should roles that are implicitly done pass tests like .does and ~~ ?
What are the reasons that they should or shouldn't?
Thanks,
/au
