use v5.14;
use Data::Dumper;

package MyClass {
	use Moo;
	has base_file => (
		is       => 'rw',
		required => 1,
		init_arg => 'base',
		builder  => sub { return 'bar' },
	);
}

# builder sub is *NOT* executed
my $object1 = MyClass2->new(base => "foo");

print Dumper($object->base_file);  # $VAR1 = 'foo'

# builder sub *IS* executed
my $object2 = MyClass->new();

print Dumper($object2->base_file);  # $VAR1 = 'bar'