Fn

Fn is a lazy Java Library that helps utilize some rudimentary functional concepts with more nounular objects.

The target audience is for developers who spend most of their time getting things done instead of learning complicated systems and intricate implementations of extractors and shying away from magical proxies and reflection.

<dependencies>
  ....
  <dependency>
    <groupId>com.iodesystems</groupId>
    <artifactId>fn</artifactId>
    <version>2.0.0</version>
  </dependency
  ....
</dependencies

Java Support

Fn supports Java 1.6, with an effort for Java 1.8 hygiene.

The Fn Object

The Fn<A> object wraps a Iterable<A> and provides extension/utility methods to make your job easier.

Because complicated actions can often be written cleaner in plain old java, the Fn object is Iterable itself, so multiple dispatching operations can be performed with ease:

for (Integer value : Fn.of(1, 2, 3).not(2).loop(2)) {
  System.out.println(value);
}

Common usages

When writing code, often we need to index or group our data

Map<String, Integer> indexed = Fn.of(1,2,3,2,3).index(new From<Integer, String>(){
    public String from(Integer integer){
        return integer.toString();
    }
});

However, this will yield a Map of size 3. If you want to preserve your groups

Map<String, List<Integer>> grouped = Fn.of(1,2,3,2,3).group(new From<Integer, String>(){
   public String from(Integer integer){
       return integer.toString();
   }
});

Iterate all the things

Enumerations, sized lists, and chained sequences are all very obnoxious when you just want to iterate across them:

Enumeration<Integer> enumeration = Collections.enumeration(Fn.list(1, 2, 3));
System.out.println("Enumerations!");
for (Integer value : Fn.of(enumeration)) {
  System.out.print(value);
}
System.out.println();

System.out.println("Sized Buckets!");
SizedIndexAccessor sizedBucket = new SizedIndexAccessor(Fn.list(1, 2, 3));
for (Integer value : Fn.of(sizedBucket, SizedIndexAccessor::getSize, SizedIndexAccessor::get)) {
  System.out.print(value);
}
System.out.println();

System.out.println("Next Containers!");
HasNext linkedItemsRoot = Fn.range(1, 3).reverse().combine(null, HasNext::new);
for (HasNext hasNext : Fn.of(linkedItemsRoot).withNext(HasNext::getNext)) {
  System.out.print(hasNext.getValue());
}
System.out.println();

Generic utilities

When getting things done, often you need to read OutputStreams into Strings, or iterate into lines:

String contents = Fn.readFully(inputStream);
for(String line : Fn.lines(inputStream));

It’s also useful to know when Strings are blank or null:

Fn.isBlank("") || Fn.isBlank(null); // true

And it’s also useful to provide an if null (and ifBlank):

Fn.ifNull(null, 3); // 3
Fn.ifBlank("", "default"); // "default"

As well as a string splitting:

assertEquals(Fn.list("a", "b", "c", ""), Fn.split("a_0b_0c_0", "_0").toList());

Tree Support

Fn includes breadth, depth, and breadthPaths, which make working on nested objects easier.

Fn.of(Node.v("value")).breadth(Node::getChildren);

Async

Async code on Java has historically been a pain, however, Fn offers Async<A> and Deferred<A> objects.

final String[] result = new String[]{null};
Fn.async(() -> "Hello world!")
    .then(new Async.Result<String>() {
      @Override
      public String onResult(String message) throws Exception {
        result[0] = message;
        return null;
      }
    });
assertEquals("Hello World!", result[0]);

The deferred example is just as simple (this example also shows progress tracking):

final String[] result = new String[]{null};
final Integer[] progress = new Integer[]{null, null};
Async.Deferred<String> defer = Fn.defer();
defer.then(new Async.Result<String>() {
    @Override
    public String onResult(String o) throws Exception {
        result[0] = o;
        return null;
    }

    @Override
    public int onProgress(int deferredProgress) {
        progress[deferredProgress - 1] = deferredProgress;
        return deferredProgress;
    }
});

defer.progress(1);
defer.progress(2);
defer.result("Hello World!");
assertEquals(result[0], "Hello World!");
assertEquals(progress[0], new Integer(1));
assertEquals(progress[1], new Integer(2));

Each async is branchable, repeatable, and any segment can run on any Executor.

When a handler uses the same Executor as it’s parent, or the INLINE executor, the handler will on the same thread as what triggered it.

When not specifying an Executor for a down stream handler, the parent’s executor will be used.