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Construction

Construction heuristic policy, nullable obligations, candidate limits, and grouped scalar construction.

Construction creates the first workable solution before local search improves it. A production config usually starts with one construction phase and then hands the result to local search.

[[phases]]
type = "construction_heuristic"
construction_heuristic_type = "first_fit"
construction_obligation = "preserve_unassigned"
value_candidate_limit = 32

Heuristic Types

Type Use
first_fit assign the first doable value that improves or preserves the current construction policy
cheapest_insertion evaluate bounded candidates and pick the cheapest insertion
list-specific constructors route and sequence initialization where list work is present

Generic FirstFit and CheapestInsertion use the canonical construction engine when matching list work is present. Pure scalar targets use the descriptor-scalar construction path.

Nullable Construction Obligation

Nullable scalar variables default to preserve_unassigned: construction may leave None in place when that is legal and scores best.

Use assign_when_candidate_exists when construction should assign a doable value whenever one exists:

[[phases]]
type = "construction_heuristic"
construction_heuristic_type = "first_fit"
construction_obligation = "assign_when_candidate_exists"

This separates Rust nullability from construction policy. A field can be nullable because later moves may unassign it, while construction can still be told to fill it whenever a legal value exists.

Candidate Limits

Scalar construction can use bounded candidates from model hooks or from config:

[[phases]]
type = "construction_heuristic"
construction_heuristic_type = "cheapest_insertion"
value_candidate_limit = 32

cheapest_insertion for scalar construction requires one bounded candidate source: either candidate_values on the model or a config candidate limit.

Construction Order Keys

Scalar construction heuristics that sort entities or values declare those capabilities on #[planning_variable]:

  • construction_entity_order_key = "fn_name"
  • construction_value_order_key = "fn_name"

SolverForge re-evaluates construction order hooks on the current working solution at every construction step. Queue-style and weakest/strongest-fit heuristics therefore track live model state instead of a phase-start snapshot.

These hooks are construction-only. Local-search scalar change, pillar-change, and ruin/recreate selectors keep canonical bounded candidate order.

Grouped Scalar Construction

Use grouped scalar construction when the legal assignment is a bundle of scalar edits.

[[phases]]
type = "construction_heuristic"
construction_heuristic_type = "first_fit"
group_name = "task_operator_assignment"
value_candidate_limit = 32
group_candidate_limit = 128

group_name selects a named model-provided scalar group. group_candidate_limit caps normalized grouped candidates after SolverForge removes illegal, duplicate, no-op, and non-frontier edits.

See Also