# value-objects-money-and-units

> Claude/Codex skill by [@zakariaf](https://omgskills.com/library/zakariaf/index.md) · 61 stars · Updated 2026-09-23

Enforces a pure-Dart value-object core that stores every quantity canonically — money as integer minor units keyed to each currency's real ISO-4217 exponent (never \*100), physical amounts as SI whole units, timestamps as UTC — and converts only at the presentation edge; forbids double/num money, cross-currency arithmetic, and defaulting an unknown currency to two decimals; routes every division of money through one largest-remainder allocate() primitive so parts always sum to the whole to the exact minor unit; derives totals instead of storing them, links entities by stable id, and injects a Clock instead of DateTime.now. Use when defining or changing Money, Currency, or a unit value object; parsing or formatting an amount; splitting, prorating, discounting, tax/tip, or distributing money; adding a currency or FX rate; converting quantities; or fixing float-money, hardcoded-100, cross-currency, off-by-a-cent, or stored-total-drift bugs.

Tags: agent-skills, ai-agents, best-practices, claude-code, codex, coding-agent, cursor, dart, dartlang, developer-tools, drift, flutter, flutter-architecture, github-copilot, go-router, llm, material-design, mvvm, riverpod, skills

## Install

```sh
git clone https://github.com/zakariaf/Flutter-Skills /tmp/Flutter-Skills && ln -s /tmp/Flutter-Skills/skills/value-objects-money-and-units ~/.claude/skills/value-objects-money-and-units
```

## From README

Value objects: money & units Store every quantity once, in one canonical form, and convert only when shown or exported. Money is integer minor units plus a currency; physical quantities are whole SI base units; time is UTC. This is what lets a user flip any display preference (currency symbol, unit system, locale) without corrupting one stored row, and lets "sum of parts == whole" be structural, not hoped-for. This core is pure Dart — no flutter/, no intl, no dart:io, no plugins. Formatting and digit normalization happen upstream/downstream, not here. These value objects live in lib/core/, the sanctioned pure-foundation layer (see project-structure-and-packages) — never a utils//common//shared/ grab-bag. Read the reference for the task at hand: references/allocate-and-splitting.md — the largest-remainder allocate() primitive, its invariants, the two-rounding-sites trap, edge policies, verified test vectors, and the subtotal→tax→tip split pipeline.

## Links

- HTML page: https://omgskills.com/library/zakariaf/flutter-skills/skills/value-objects-money-and-units/
- GitHub: https://github.com/zakariaf/Flutter-Skills
- Author: [@zakariaf](https://omgskills.com/library/zakariaf/index.md)

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