ADR-0005 — Settings are bound by derivation

type: adr status: Accepted tags: [adr]

Context

A program declares its settings as a record. Reading each field from a variable by hand repeats the field list in code that drifts from the type, and Pudu's derive strategies read a record's fields, types, and attributes at compile time.

Decision

[[src/PuduLangEnvironment/Binding]] declares Bind and Redacted with derive strategies for records. A field's variable is named by @env("NAME") or by its name in upper snake case, @default("text") fills an unset one, and @secret hides it from redacted(). Each field type reads its text through the Variable trait, implemented for text, numbers, truth values, secrets, and options of those. [[src/PuduLangEnvironment/Settings]] runs the derived bind and the validator together ([[decisions/ADR-0004-settings-through-the-validator]]).

Consequences

• Adding a setting is adding a field.
• The fluent Configuring chain stays hand-written: its methods carry meaning (withProbe() picks a depth, withEnvironment(name) sets two fields, withFiles(&[]) restores the default) that a per-field derive cannot express.

Rejected

• A caller-supplied build function: the mapping repeated by hand.
• A key-to-field table: names checked only at run time.

Referenced by

[[CHANGELOG]] · [[decisions/_MOC]] · [[handoffs/2026-10-07-initial-package]] · [[src/PuduLangEnvironment/Settings]]