When to use generics

Re:When to use generics by azth on Tuesday April 12, 2022 @09:22PM (#31010201)

> If you have an interface with a single method, or something with a single varying piece of behavior, please strongly consider accepting a function instead.

Java neatly solves this by means of Functional Interfaces. Interfaces that have a single method related to the generic type parameter can be called by using lambda syntax. Take for example sorting:

   <T> void sort(T[] a, Comparator<? super T> c)

A `Comparator<T>` has a method `int compare(T o1, T o2)`, which allows the caller to invoke `Arrays.sort` by passing a lambda:

    Arrays.sort(list, (l1, l2) -> l1.compareTo(l2));

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Re:When to use generics by Groxx on Tuesday April 12, 2022 @09:32PM (#31010258)

I don't think I'd call this "neatly"... more "a weird but pragmatic hack to improve an incredibly common pattern that had no concise option prior to java 8". And it kinda encourages continuing the "keep declaring a lambda that could have just been a function reference if the API had used a function instead" pattern, which is not great.

But I do very much like it. It improves Java's ergonomics quite a lot.

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Re:When to use generics by layer8 on Tuesday April 12, 2022 @10:12PM (#31010507)

What I like about Java functional interfaces is that they give a place to specify an interface contract. For example, with Comparator, it specifies that instances must implement a total ordering. Purely structural function types don't have that affordance.

A slightly problematic point, however, is that you can assign a method reference from one functional interface to a variable of another functional interface based purely on structural typing, even if they happen to have incompatible interface contracts. For example, if you had a PartialOrder functional interface with the same parameter/return types as Comparator, then you could assign PartialOrder::compare to a Comparator variable although the semantics aren't compatible. Whereas nominal typing prevents you from assigning a PartialOrder to Comparator (no "duck typing"), Java circumvents the nominal type system here for method references, with the result that one may assign incompatible implementations without noticing.

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Re:When to use generics by watwut on Wednesday April 13, 2022 @02:54AM (#31011892)

> keep declaring a lambda that could have just been a function reference

Yes, but those are less readable, too much syntax and not enough javadoc/names on them.

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