Func-helper

Functional helpers for Java

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Functional helpers for java

This project is a really simple functional library. It provides only the building blocks that I lacked while working on a project. It is mostly inspired by what I've seen and used in the Scala language.

Get it

<dependency>
    <groupId>fr.sertelon.fp</groupId>
    <artifactId>func-helper</artifactId>
    <version>2.0.0</version>
</dependency>

Features

Opt

Option[T] is a very handy structure in Scala. Guava has its own Optional, but I didn't want to depend on any big lib. Thus, Opt

public class Option {

    Function<Integer, String> intToString = input -> String.valueOf(input);

    Function<String, Boolean> isEmpty = input -> input.isEmpty();

    public Option() {

        Opt<Integer> intOpt = toOpt(null); // => None
        Opt<Integer> intOpt2 = toOpt(3);   // => Some(3)

        Opt<Integer> choose = intOpt.or(intOpt2); // => Some(3)

        Opt<String> map = choose.map(intToString); // => Some("3")

        map.isDefined(); // => true
        intOpt.getOrElse(3); // => 3
        intOpt.get(); // => NoSuchElementException
        Opt<String> strOpt = toOpt((Object) "3").asOpt(String.class);
        toOpt("").filter(isEmpty); // => None       

        Opt<Integer> noneOpt = none();
    }
}

IList

This construct is an immutable linked list. It is based on the same implementation as Scala's List.

public class ImmutableList {

    public ImmutableList() {
        nil();  // => empty list
        IList<Integer> l = list(1, 2, 3); // => List(1,2,3)
        range(0, 3); // List(0,1,2)
        rangeIncl(0, 3); // List(0,1,2,3)

        l.get(1); // => 2
        l.head(); // => 1
        l.tail(); // => List(2,3)
        l.isEmpty(); // => false
        l.reverse(); // => List(3,2,1)
        l.mkString("-"); // => 1-2-3
        l.mkString("[", ":", "]"); // => [1:2:3]
        l.prepend(0); // => List(0,1,2,3)

        l.map(intToString); // => List("1","2","3")
        l.filter(isOdd); // => List(1,3)
        l.foreach(print); // => prints 1, then 2, then 3
        l.foldLeft(0, sum); // => 6
    }

    Function<Integer, String> intToString = input -> String.valueOf(input);

    Function<Integer, Boolean> isOdd = input -> input % 2 == 1;

    Function<Integer, Nothing> print = input -> {
        System.out.println(input);
        return nothing;
    };

    BiFunction<Integer, Integer, Integer> sum = (i1, i2) ->  i1 + i2;
}

Try

This structure allows you to return success or failure information.

public class TryStructure {

    public TryStructure() {

        Try.emptySuccess(); // => Success<Nothing>(nothing)
        Try.failure(new Exception()); // => Failure<Exception, Object>
        Try.success(Integer.valueOf(2)); // => Success<Integer>(2)

        strToDouble.apply("2.34"); // => Success<Double>(2.34)
        strToDouble.apply("xxxx"); // => Failure(NumberFormatException, Double>

        strToDouble.apply("2.34").map(doubleToStr); // => Success<String>("2.34")

        IList<Try<Integer>> l = list(success(1), success(2), success(3));

        Try<IList<Integer>> tl = Try.sequence(l); // => Success(List(1,2,3)) 
    }

    FTry1<String, Double> strToDouble = input -> {
        try {
            return success(Double.valueOf("xxx"));
        } catch (NumberFormatException e) {
            return failure(e);
        }
    };

    FTry1<Double, String> doubleToStr = input -> Try.success(input.toString());

}

Utils

public class Utils {

    public Utils() {
        // Tuple2
        T2<String, Long> tuple = t2("hello", 2L);
        String hello = tuple._1; // "hello"
        Long two = tuple._2; // 2

        // Predef functions. Useful functions commonly used
        Predef.isStrEmpty.apply(""); // true
        Predef.isStrNotEmpty.apply(""); // false
        Predef.objToString.apply(2); // "2"
    }

}

Roadmap

If someone else than me is to use this library, I'm open to feedback! Will add whatever I'd like to use in Java, as long as I can keep this lib lightweight, otherwise, I should be better off using an existing one.

License

This software is licenced under the Apache Software License v2.0, you can find it in the LICENCE file.