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

setattr(foo, field, 42);
print(getattr(foo, field)); # expect: 42

var x = "b";
x = x + "ar";
setattr(foo, field, 20);
print(getattr(foo, x)); # expect: 20
print(foo.bar); # expect: 20

print(getattr(foo, "field")); # expect runtime error: Undefined property 'field'.