yield4j

yield4j adds generator methods to Java through annotation processing magic.

Currently, yield4j must be both a compile-time dependency and a runtime dependency. That may change in the future.

Here's an example of a generator method that generates numbers from the Fibonacci sequence:

public class Fibonacci {
    @Generator
    public Iterable<Integer> fib() {
        yield_return(0);
        yield_return(1);
        int i1 = 0, i2 = 1;
        while (true) {
            int next = i1 + i2;
            yield_return(next);
            i1 = i2;
            i2 = next;
        }
    }
}

Return a value from a generator

Use yield_return(X) to generate value X. The yield_return method is a static method of org.yield4j.YieldSupport.

Stop generating values

To stop/quit the generator, use yield_break().

Rules

• A generator method cannot contain a normal return statement.
• No yielding within a synchronized statement (generator methods can be synchronized, though).
• yield_break cannot be used in a finally statement.
• yield_return cannot be used in a catch or finally statement.

In general, the yield_* statements behave much as their C# counterparts.

A note on finally

Code in a finally statement may not be executed if a generator is stopped before execution reaches that point.

Supported Java versions

yield4j works with Java 6, 7 and 8. It was a while ago I tested with Java 8, so it may be shaky there.

To compile and test with all currently installed Java versions on Windows, run buildall.bat. Maven is required.

Compilation

Just include the yield4j JAR in the class path. Make sure to not turn off annotation processing.

TODO

See the TODO file.

A big TODO is to add some sort of editor/IDE support...

License

MIT license. See LICENSE.md.