Generating tuples containing Long for Vavr Property Checking

Question

I need a pair of random longs for property checking with Vavr.

My implementation looks like this:

Gen<Long> longs = Gen.choose(Long.MIN_VALUE, Long.MAX_VALUE);
Arbitrary<Tuple2<Long, Long>> pairOfLongs = longs
        .flatMap(value -> random -> Tuple.of(value, longs.apply(random)))
        .arbitrary();

Is any better/nicer way to do the same in vavr?

Answer 1

Arbitrary<T> can be seen as a function of type

int -> Random -> T

Generating arbitrary integers

Because the sample size is of type int, it would be natural to do the following:

Arbitrary<Tuple2<Integer, Integer>> intPairs = size -> {
    Gen<Integer> ints = Gen.choose(-size, size);
    return random -> Tuple.of(ints.apply(random), ints.apply(random));
};

Let's test it:

Property.def("print int pairs")
        .forAll(intPairs.peek(System.out::println))
        .suchThat(pair -> true)
        .check(10, 5);

Output:

(-9, 2)
(-2, -10)
(5, -2)
(3, 8)
(-10, 10)

Generating arbitrary long values

Currently we are not able to define a size of type long, so the workaround is to ignore the size and use the full long range:

Arbitrary<Tuple2<Long, Long>> longPairs = ignored -> {
    Gen<Long> longs = Gen.choose(Long.MIN_VALUE, Long.MAX_VALUE);
    return random -> Tuple.of(longs.apply(random), longs.apply(random));
};

Let's test it again:

Property.def("print long pairs")
    .forAll(longPairs.peek(System.out::println))
    .suchThat(pair -> true)
    .check(0, 5);

Output:

(2766956995563010048, 1057025805628715008)
(-6881523912167376896, 7985876340547620864)
(7449864279215405056, 6862094372652388352)
(3203043896949684224, -2508953386204733440)
(1541228130048020480, 4106286124314660864)

Interpreting an integer size as long

The size parameter can be interpreted in a custom way. More specifically we could map a given int size to a long size:

Arbitrary<Tuple2<Long, Long>> longPairs = size -> {
    long longSize = ((long) size) << 32;
    Gen<Long> longs = Gen.choose(-longSize, longSize);
    return random -> Tuple.of(longs.apply(random), longs.apply(random));
};

However, the last example does not match the full long range. Maybe it is possible to find a better mapping.

Disclaimer: I'm the author of Vavr (formerly known as Javaslang)