Generator to Iterator Converter

This tool compiles generator methods to Java-style iterators.

Generator methods are a very convenient way to write code that produces streams of values: they are normal functions that periodically yield values to the caller. In many cases it is easier to express a stream of values as a generator than to manually write an implementation of Iterator.

For example, a generator method to produce Fibonacci numbers might look like this:

int a = 1;
int b = 1;
while (true) {
    yield(a);     // produce a value
    int prev_a = a;
    a = b;
    b += prev_a;
}

Using the tool

I expect you to be running Python 3. Install dependencies with pip:

$ pip3 install -r requirements.txt

Invoke the tool by running:

$ python3 -m gen2it INPUT_FILE -o OUTPUT_FILE

The input should be a Java source file with a single class having a TypeName generate(args...) method. That method may call yield(TypeName value) to yield values. The output is a Java source file with boolean hasNext() and TypeName next() methods.

Sample inputs for the tool can be found in the examples folder.

Usage Notes

• The generated iterators are not threadsafe. You will need to manually synchronize calls to any method on the generated iterator classes.

• This style of programming can be faked in pure Java using threads, however, this tool will avoid the overhead of the extra threads and the risks of leaking memory through them.

• Many features are not yet implemented. Feel free to file issues or open pull requests to fix missing functionality. A few things that may not work properly yet:

  • try-catch and try-with-resources
  • for-loops
  • using a for-each loop over an array