# Display Objects

## Definition

A **Display Object** encapsulates **reusable, UI-only display logic**.

It answers the question:

> “How should this specific piece of information be shown?”

Display Objects are **not screen-specific**.
They exist to avoid duplicating presentation logic across View Models.

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## Responsibilities

A Display Object MAY:

- format values (money, dates, durations)
- handle localization and language-specific rules
- map codes to labels
- encapsulate UI display conventions
- be reused across multiple View Models

A Display Object MUST:

- be deterministic
- be side-effect free
- operate only on presentation data

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## Restrictions

A Display Object MUST NOT:

- contain business logic
- enforce domain invariants
- perform validation
- influence system behavior
- be sent back to the server
- depend on backend or infrastructure concerns

If a rule affects system correctness or persistence,
it does not belong in a Display Object.

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## Ownership & Placement

- Display Objects belong to the **presentation layer**
- They are frontend-only
- They are not shared with the backend or core

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## Relationship to View Models

- View Models MAY use Display Objects
- Display Objects MUST NOT depend on View Models
- Display Objects represent **parts**
- View Models represent **screens**

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## Testing

Display Objects SHOULD be tested because they often contain:

- locale-specific behavior
- formatting rules
- edge cases visible to users

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## Summary

- Display Objects encapsulate **how something looks**
- View Models encapsulate **what a screen needs**
- Both are presentation concerns
- Neither contains business truth