class Foo {}
var foo = Foo();
var field = "bar";

foo.bar = "42";
print(foo.bar); # expect: 42
print(hasattr(foo, "bar")); # expect: true

delattr(foo, "bar");
print(hasattr(foo, "bar")); # expect: false

foo.bar = "42";
delattr(foo, field);
print(hasattr(foo, "bar")); # expect: false

delattr(foo, field); # expect runtime error: Undefined property 'bar'.