# Runtime Fields

Runtime Fields provide reactive and computed values used inside features.

They are used to derive state from configuration, cache computed results, and react to changes.

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### Overview

Runtime Fields are used to:

* derive values from configuration
* cache computed state based on a key
* detect and react to value changes

They are commonly used together with `ConfigWatcher` and `OmsFeature`\
See [ConfigWatcher](/oms-wiki/developer-guide/core-architecture/feature-system.md#configwatcher)\
See [OmsFeature](/oms-wiki/developer-guide/core-architecture/feature-system.md#omsfeature)

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### Core Types

#### CachedField

`CachedField` represents a key-based cached value.

The value is recomputed when the key changes and can optionally:

* validate computed values
* notify on updates
* be observed during runtime

{% @github-files/github-code-block url="<https://github.com/c0nnor263/OperateMyServer/blob/main/oms-api/src/main/kotlin/io/conboi/oms/api/foundation/CachedField.kt>" %}

***

### Usage

Runtime Fields are typically used inside features to:

* compute derived values from config
* track changes in configuration-dependent state
* avoid recomputing expensive logic

Fields are usually defined using a builder-style configuration.

***

### Notes

* Values are recomputed only when the key changes
* Fields can trigger update callbacks
* Observation is controlled via `watch()`
* Integrated with `ConfigWatcher` by providing an wrapper `configField`


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