Macro impl_flatmap_step 

macro_rules! impl_flatmap_step {
    ($step:ty, $name:literal) => { ... };
}

Helper macro to implement Step for flatmap steps (1:N mappings).

Flatmap steps expand each input traverser into zero or more output traversers. The step struct must:

• Implement Clone
• Have an expand(&self, ctx: &ExecutionContext, traverser: Traverser) -> impl Iterator<Item = Traverser> method
• Have an expand_streaming(&self, ctx: &StreamingContext, traverser: Traverser) -> Box<dyn Iterator<Item = Traverser> + Send + 'static> method

Example

#[derive(Clone)]
struct DuplicateStep {
    count: usize,
}

impl DuplicateStep {
    fn expand(&self, _ctx: &ExecutionContext, traverser: Traverser) -> impl Iterator<Item = Traverser> {
        (0..self.count).map(move |_| traverser.clone())
    }

    fn expand_streaming(&self, _ctx: &StreamingContext, traverser: Traverser) -> Box<dyn Iterator<Item = Traverser> + Send + 'static> {
        let count = self.count;
        Box::new((0..count).map(move |_| traverser.clone()))
    }
}

impl_flatmap_step!(DuplicateStep, "duplicate");