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Problem Facts

Immutable input data and derived list-element shadow state used by constraints.

A problem fact supplies immutable input data. The solver reads those inputs when evaluating constraints. Examples include employees, rooms, timeslots, and vehicle visits.

List elements may also carry configured derived shadows such as owner, index, previous, or next. Those fields are maintained by the score director, not independent planning decisions. Generated sources for such collections receive incremental element notifications when owner lists change; ordinary fact collections remain static. See List Variables.

The #[problem_fact] Macro

use solverforge::prelude::*;

#[problem_fact]
pub struct Employee {
    #[planning_id]
    pub id: usize,
    pub name: String,
    pub skills: Vec<String>,
}

#[problem_fact]
pub struct Timeslot {
    #[planning_id]
    pub id: usize,
    pub day_of_week: String,
    pub start_time: String,
    pub end_time: String,
}

Field Attributes

#[planning_id]

Provides stable identity for the fact. This is recommended whenever the fact is referenced by a planning variable or appears in analysis output.

#[planning_id]
pub id: usize,

When to Use Problem Facts vs Planning Entities

  Problem Fact Planning Entity
Modified by solver? No Yes
Has planning variables? No Yes
Example Employee, Room, Timeslot Shift, Lesson, Visit
Role Input data / possible values Things being assigned

A common pattern is to use a problem-fact collection as the named value range for a planning variable:

#[planning_entity]
pub struct Shift {
    #[planning_id]
    pub id: usize,

    #[planning_variable(value_range_provider = "employees", allows_unassigned = true)]
    pub employee_id: Option<usize>,
}

#[planning_solution]
pub struct Schedule {
    #[problem_fact_collection]
    pub employees: Vec<Employee>,

    #[planning_entity_collection]
    pub shifts: Vec<Shift>,

    #[planning_score]
    pub score: Option<HardSoftScore>,
}

Requirements

  • Must be a named Rust struct

The macro provides the standard derives and trait impls automatically.

See Also