Trait Operator 

pub trait Operator: Debug {
    // Required methods
    fn schema(&self) -> &Schema;
    fn next(&mut self) -> Result<Option<Chunk>>;
}

A source of chunks.

Two methods, and the reason there are only two is that everything else an operator could be asked is either a property of its schema or a property of the plan it came from. An operator that needed a third method to be driven would be an operator the scheduler has to know the shape of, and section 7.2’s morsel driven scheduler is supposed to know only that a pipeline has a source, some streaming operators and a sink.

next returning Some with an empty chunk is allowed and means nothing more than that this call produced no rows, which is what a filter that rejected a whole batch does. Only None means the operator is finished. Calling next again after None returns None again for every operator here, which is what makes a driver loop safe to write as a while let.

Required Methods

fn schema(&self) -> &Schema

The columns this operator produces.

fn next(&mut self) -> Result<Option<Chunk>>

The next batch, or None when there are no more.

Errors

Anything an expression, a cast or a kernel reports, carrying the message the user sees.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors