5 ms·

Once I tried to make a union of a sorted set and an unsorted one. Result set inherits behaviour of a bigger input set so when i first got my sometimes-sorted se

by nidu 10y ago

Once I tried to make a union of a sorted set and an unsorted one. Result set inherits behaviour of a bigger input set so when i first got my sometimes-sorted set i thought like loosing my mind.

village-idiot 10y ago
Oh, that's really annoying too.
dilap 10y ago
Avoiding madness like this is why I have come to really prefer statically typed languages.
- masklinn 10y ago
  The issue doesn't have much to do with dynamic typing, any subtyping support can trigger it. Take Java, if Set had a `Set union(Collection)` method a SortedSet could return a new SortedSet (cast as a set, but still with the actual behaviour of a sorted set).
  - sanderjd 10y ago
    But you would not be able to pass it to a method that takes a SortedSet, which means you can't rely on the sorted behavior. Incorrectly using behavior that your implementation doesn't support is where the confusion comes from, it doesn't come from your implantation having extra behavior that you can't use.
  - yawaramin 10y ago
    In Java, you can have: class Set<A> { public Set<A> union(Collection<A> c) { ... } } class SortedSet<A> extends Set<A> { @Override public SortedSet<A> union(Collection<A> c) { ... } } In other words, the more specific type overrides the operations of the more general type into more specialised operations.
  - dilap 10y ago
    defnly agree that you can get these problems in languages with static types, but i think you have to go out of your way vs dynamic languages, where these types of shenanigans are easier and (in my experience) prevalent. e.g., in your example, because your returned type is Set, you presumably would not be relying on the result to be a sorted set! -- so there would be no problem. if you WERE relying on it being a sorted set, you would have to explicitly downcast -- i.e. would pointing a gun and at your foot and pulling the trigger. maybe you know it's unloaded, but the danger is clear from the type system. ;)

by nidu 10y ago

Once I tried to make a union of a sorted set and an unsorted one. Result set inherits behaviour of a bigger input set so when i first got my sometimes-sorted set i thought like loosing my mind.

village-idiot 10y ago

Oh, that's really annoying too.

dilap 10y ago

Avoiding madness like this is why I have come to really prefer statically typed languages.

masklinn 10y ago
The issue doesn't have much to do with dynamic typing, any subtyping support can trigger it. Take Java, if Set had a `Set union(Collection)` method a SortedSet could return a new SortedSet (cast as a set, but still with the actual behaviour of a sorted set).
- sanderjd 10y ago
  But you would not be able to pass it to a method that takes a SortedSet, which means you can't rely on the sorted behavior. Incorrectly using behavior that your implementation doesn't support is where the confusion comes from, it doesn't come from your implantation having extra behavior that you can't use.
- yawaramin 10y ago
  In Java, you can have: class Set<A> { public Set<A> union(Collection<A> c) { ... } } class SortedSet<A> extends Set<A> { @Override public SortedSet<A> union(Collection<A> c) { ... } } In other words, the more specific type overrides the operations of the more general type into more specialised operations.
- dilap 10y ago
  defnly agree that you can get these problems in languages with static types, but i think you have to go out of your way vs dynamic languages, where these types of shenanigans are easier and (in my experience) prevalent. e.g., in your example, because your returned type is Set, you presumably would not be relying on the result to be a sorted set! -- so there would be no problem. if you WERE relying on it being a sorted set, you would have to explicitly downcast -- i.e. would pointing a gun and at your foot and pulling the trigger. maybe you know it's unloaded, but the danger is clear from the type system. ;)