[jargonjustin]

Java's Comparator type is more general (you don't necessarily need to project the type for comparison) and an existing abstraction. It's not hard to introduce a combinator to transform the representation as a library, as in:

    countries.sorted(by(x -> x.population)).limit(3).map(x -> x.name)

where `by` looks something like:

    <S, T> Comparator<T> by(Projection<S, T> projection);

    interface Projection<S, T> {
       Comparable<S> project(T value);
    }

[barrkel]

Sure; and you'd have to import the thing that contains 'by'.

It's still ugly, and would prevent e.g. a radix sort being used when projecting an integer as the sort key, or American flag sort for strings.

[javafu2]

It already exists in the API. Your type Projection is a Function, and by is called comparing in interface Comparator.

so one can write: ``` contries.sorted(comparingInt(Country::getPopulation)). ... ```