Joiners

Joiners define the matching criteria when two streams are joined. Without joiners, a join produces every possible pair — joiners filter this down to only relevant combinations.

Available Joiners

equal

For self-joins (pairing items from the same collection), takes a single key extractor:

equal(|shift: &Shift| shift.employee_idx)

equal_bi

For cross-joins (pairing items from two different collections), takes two key extractors:

equal_bi(|shift: &Shift| shift.employee_idx, |u: &Unavailability| u.employee_idx)

less_than

Matches when the left value is less than the right. Takes two extractors.

less_than(|a: &Shift| a.id, |b: &Shift| b.id)

greater_than

Matches when the left value is greater than the right. Takes two extractors.

greater_than(|a: &Shift| a.priority, |b: &Shift| b.priority)

overlapping

Matches when two ranges overlap. Takes four extractors: start and end for each side.

overlapping(
    |a: &Shift| a.start_time, |a: &Shift| a.end_time,
    |b: &Shift| b.start_time, |b: &Shift| b.end_time,
)

filtering

A general-purpose joiner that uses a predicate over both elements.

filtering(|a: &Shift, b: &Shift| a.location.distance_to(&b.location) < 50.0)

Using Joiners with join

Self-join — pass a single equal joiner directly:

factory.for_each(|s: &Schedule| s.shifts.as_slice())
    .join(equal(|shift: &Shift| shift.employee_idx))

Cross-join — pass a tuple of (extractor, joiner):

factory.for_each(|s: &Schedule| s.shifts.as_slice())
    .join((
        |s: &Schedule| s.unavailability.as_slice(),
        equal_bi(|shift: &Shift| shift.date, |u: &Unavailability| u.date),
    ))

Performance Note

Indexed joiners (equal, equal_bi, less_than, greater_than, overlapping) are much faster than filtering because they use index lookups instead of iterating all pairs. Prefer indexed joiners where possible and only use filtering for conditions that can’t be expressed with indexed joiners.

See Also

• Constraint Streams — The core stream API
• docs.rs/solverforge — Full joiner API reference