id: ADR-0010 title: Adopt D7: balance, costing and utility laws are templates expanded over a contributions substrate status: accepted date: 2026-09-13 deciders: [paul-heyse] level: decision principles: [DM-16, DM-17, DM-18, DM-25] blueprint: [§D7, §10.1, §10.2] review: not-required: neither review raised a finding against D7 evidence: Proposed supersedes: [] superseded-by: null revisit: A law family cannot be expressed over contributions and needs a compiler rule of its own verification: tests/conformance law-expansion golden tests per control-volume variant

ADR-0010: Adopt D7: balance, costing and utility laws are templates expanded over a contributions substrate

Context

Blueprint D7 makes material, energy, momentum, element and charge balances, and the costing and utility-minimization laws, instances of law templates expanded over a contributions substrate by the generic compiler. Control volumes are template compositions that declare which contributions exist.

Scope

Binds how conservation laws are expressed. The contribution kinds themselves are §10.2.

Drivers

IDAES writes one build() per balance variant; the variants differ only in which contributions exist; extension locality (charter §E) asks for one authoritative addition per new law.

Options

One template per balance variant — rejected: the combinatorics of 0D/1D by phase/element/charge is exactly what IDAES pays for. A general equation authoring surface with no law concept — rejected: the balance structure is what diagnostics and scaling reason over.

Outcome

Laws are templates; control volumes compose them by declaring their contributions; the generic compiler expands them (§10).

Consequences

A new contribution kind is a registry addition; a new law family is usually a template, not code (§22.3).

Compensating controls

Golden expansion tests per control-volume variant; the closure report’s balance category is open while any law has unmatched contributions.

Confirmation

rust / test runs the conformance layer; slice A and slice B acceptance (§24.2) exercise the lumped and distributed variants.

Pros and cons

Templates are indirection; the alternative is the maintenance surface D2 exists to remove.

More information

Blueprint §D7, §10.1 (conservation law template), §10.3-§10.4 (control volumes), §11 (unit model library).

Status history

• 2026-09-13 — accepted with the repository-seeding pull request (backfilled from blueprint revision 3).